KAPLAN, J.

The school committee and superintendent of schools of Malden, defendants, appeal from a final decree against them in declaratory suits brought by two teachers in the Malden public schools. The questions relate to so called "maternity leave" and our task has been lightened by recent decisions of the Supreme Court of the United States on the constitutional aspects of that subject. See Cleveland Bd. of Educ. v. LaFleur, and the companion case Cohen v. Chesterfield County Sch. Bd. 414 U.S. 632 (1974).

The facts of the present appeals are set out mainly in statements of agreed facts and stipulations of the parties. The plaintiffs, Mrs. Francine Black and Mrs. Kathleen M. Lane, were engaged as teachers by the Malden school department in September, 1964, and after September, 1967, they qualified under the provisions of G.L.c. 71, § 41, as teachers serving "at discretion," i.e., with tenure. It can be surmised that their pregnancies occurred in late June or early July, 1968. Early in November, 1968, they severally informed the superintendent of schools that they were pregnant and requested leaves of absence on that account to commence on January 2, 1969.

In purported response to these requests the school committee voted at its meeting on November 12, 1968, to accept the plaintiffs' "resignations" effective December 31, 1968, "in view of the fact" — as the superintendent wrote — that "leaves of absence are not granted for maternity reasons." Although the letters did not refer expressly to any rules of the school committee, they were a reflection of c. IV, § 15, of those rules, providing that a married teacher must resign her position at the end of the fourth month of pregnancy, and, further, that she was then not eligible for reinstatement until six months after the birth of her child. The text of § 15 is reproduced in the margin.

The plaintiffs answered the committee promptly, denying that they had ever offered to "resign" or that the school committee had any authority to accept their "resignations." They said they were withdrawing their requests for leaves and intended to continue to carry out their teaching duties. Early in December, 1968, the plaintiffs filed complaints with the Massachusetts Commission Against Discrimination (MCAD) alleging that the school committee had discriminated against them on the ground of sex, but they continued to teach through January 31, 1969, after which they absented themselves. They received paychecks through March 10, 1969, which evidently included sick pay for thirteen consecutive teaching days after January 31 on which they were absent (plus pay for other benefits). These March checks were the last they received, and they have not taught in the Malden schools since.

Rather inconsistently with the attitude shown in the vote of November 12, 1968, the superintendent of schools wrote to the plaintiffs on March 11, 1969, quoting from the school committee's rules as to sick leave and requesting a physician's certificate of disability with respect to their absence. The plaintiffs complied with the request by furnishing letters from their physicians stating that they were under doctors' care and unable to work at the time. But on March 21, 1969, the superintendent wrote to the plaintiffs advising them that sick leave benefits did not extend to pregnancy and "terminating" their employment as of that date. Mrs. Black's child was born on April 4; Mrs. Lane's on March 30.

On April 7, 1969, MCAD's investigating commissioner notified the superintendent of schools that he had made a finding of probable cause in respect to the complaints and he suggested terms of conciliation which included a revocation of the termination order of March 21, 1969, a six months' maternity leave retroactive to January 31, 1969, with a right to return by July 31, 1969, with benefits, if the teachers manifested acceptance by that date, and payment of $250 to each of them for expenses and inconvenience incurred. The commissioner asked for a response from the Malden authorities by April 16, 1969. The school committee, however, took no action until July 1, 1969, when it voted to accept the MCAD terms and so informed the plaintiffs and the commission. The plaintiffs did not concur. The retroactive six month leave would have required them to repay the money received for the period following January 31, 1969 (more than $900 in each case), meaning in effect that they would not receive any sick pay during the period of the proposed maternity leave.

There were no further proceedings before the MCAD. In the impasse the teachers commenced in the Superior Court actions of mandamus later amended by leave of court into petitions for declaratory and consequential relief. The suits eventuated in the final decree under review (covering both cases) declaring the dismissals of the plaintiffs from employment to be illegal and a nullity, ordering reinstatement of the plaintiffs at the pay scale and with the seniority and other benefits they would otherwise have attained, and awarding Mrs. Black a total of $41,144 for unpaid salary to the time of decree and interest thereon and expenses of suit — see G.L.c. 71, § 43B — and making a like award to Mrs. Lane of $45,939.49.

1. In their argument in this court the defendants suggest that the present actions are barred because of the institution of the MCAD proceedings. General Laws c. 151B sets out an administrative procedure for enforcement of the anti-discrimination statutes of the Commonwealth. See our recent decision in East Chop Tennis Club v. Massachusetts Commn. Against Discrimination, 364 Mass. 444, 446-448 (1973). The sense of c. 151B, § 9, is that recourse to judicial remedy for an alleged unlawful practice within the statute (see § 4) is precluded when MCAD proceedings are pending covering the same grievance. But the MCAD complaints, filed more than three months before the termination letters of March 21, 1969, concerned only the failure of the school committee to grant the plaintiffs leaves of absence for pregnancy and the committee's attempted acceptance of the plaintiffs' nontendered resignations. In contrast, the plaintiffs' suits complained of the March 21 dismissals and looked to reinstatement with back pay. The investigating commissioner's conciliation proposal was an effort to resolve the entire controversy which had become significantly enlarged since the filing of the MCAD complaints. It may be questioned whether the Commissioner could thus on his own motion extend the matters which had been confided to the commission and by that means foreclose the plaintiffs' recourse to judicial remedies. In all events the administrative proceedings ceased when the conciliation proposal failed of acceptance. At that point it was up to the commission, under c. 151B, § 5, to issue its own notice calling for a hearing (or commence a suit in equity in the Superior Court). The commission did not act, and no further steps have been taken over a period of more than four years. In fact it appears that all concerned viewed the resort to MCAD as moot or abandoned after negotiations broke down and the plaintiffs had presented to the court the basic issue of the legality of the Malden rules with its constitutional implications. As § 9 is not applicable on these facts, we need not inquire whether, having omitted to raise in the court below, as a ground for abating the present suits, the issue of the plaintiffs' failure to pursue the administrative process, the school committee may be heard to make that contention for the first time in this court. Cf. Westland Housing Corp. v. Commissioner of Ins. 346 Mass. 556, 557 (1963); Massachusetts Mut. Life Ins. Co. v. Massachusetts Life Ins. Co. 351 Mass. 283, 285, 289 (1966).

2. By its letters of March 21, 1969, the school committee unilaterally "terminated" the plaintiffs' employment. The plaintiffs argue that the terminations were acts of "dismissal" of tenured teachers within G.L.c. 71, § 42, and illegal because they were not preceded by notice and hearing and accompanied by the other procedural safeguards envisaged by this fundamental statutory provision. It is agreed that the defendants did not purport to comply with that statute, but they maintain that what was involved in each case was a "forced resignation" (as they call it) under the rule as to pregnancy quoted in n. 3 above, and so § 42 did not apply.

The letters of March 21 were abrupt and flat, susceptible of the meaning that the plaintiffs were absolutely terminated without any chance of reinstatement, possibly because of their refusal to resign and quit work as required by the rule. The plaintiffs point out that the school committee has never affirmatively invited them to return. All this looks like "dismissal." But we think the letters are rather to be construed as a final though belated decision by the school committee, after internal deliberations, to enforce their rule, especially as to reinstatement. Indeed, in the case of the plaintiff Lane the statement of agreed facts makes it explicit that the termination was in accordance with the rule requiring the pregnant teacher to resign, which implies rights of later reinstatement.

Seen in this light, the terminations were not dismissals within § 42, for that section deals with complete separation from the job. See, e.g., Boody v. School Comm. of Barnstable, 276 Mass. 134, 138 (1931); Downey v. School Comm. of Lowell, 305 Mass. 329, 331 (1940). Cf. Western Elec. Co. Inc. v. Director of Div. of Employment Security, 340 Mass. 190 (1960). The point is reinforced by the statement in § 42 that that section shall not affect the right of the committee to dismiss a teacher whenever a decrease in the number of pupils in the schools renders such action advisable, and the further statement that no teacher lawfully dismissed shall receive compensation for services rendered thereafter. To be sure, for a teacher to be "dismissed," he need not be wholly banished from the school system; it is exclusion from the job or "category" that counts. Thus in McCartin v. School Comm. of Lowell, 322 Mass. 624 (1948), the removal of a superintendent of schools from his post as such was held to be a dismissal although he was offered a position as a teacher. On the other hand, a party in that case who had been demoted from principal to teacher was held not dismissed because the demotion was thought to involve only a shift of duties, a principal being merely a superior sort of teacher. (But see, now, G.L.c. 71, § 42A, as to demotion of principals.)

In saying that § 42 did not control on the present facts, we are aware that the terminations might involve a sizeable postponement of the plaintiffs' resuming their jobs. Unless there was a waiver of the normal six-month waiting period, these plaintiffs would not be eligible for reinstatement until October, 1969, at the earliest, and then their reinstatement was subject to contingencies that might defer their reentry into the system for a considerable period. Nor can it be said that it would necessarily have been futile to accord the plaintiffs § 42 procedural rights because the fact of their pregnancy was not fairly debatable, cf. Jantzen v. School Comm. of Chelmsford, 332 Mass. 175 (1955); Kaplan v. School Comm. of Melrose, 363 Mass. 332 (1973), for at a hearing the plaintiffs might have argued the question of "good cause," possibly resulting in a committee decision to revise its rule to constitutional norms. (Excerpts from the minutes of the committee during this period, which appear of record, indicate that there was sentiment favoring change.) Still we think § 42 was inapplicable; and the plaintiffs do not contend that the terminations ran afoul of any other statutory procedure.

3. Apart, however, from matters of procedure, we think the terminations were in substance illegal to the point of unconstitutionality. Questions of this order were making their way through the lower courts as the present controversy developed and have now been dealt with by the Supreme Court opinions in the Cleveland and Chesterfield County school cases.

In outline, the Supreme Court held that school board regulations not materially different from Malden's, requiring that teachers cease teaching and take leave as early as four or five months before the expected date of birth, and materially trammeling the teachers' eligibility to return to work, offended the due process clause of the Fourteenth Amendment. The court found that such rules, by "acting to penalize the pregnant teacher for deciding to bear a child," put a heavy burden on the "freedom of personal choice in matters of marriage and family life [that] is one of the liberties protected by the Due Process Clause" against needless, arbitrary, or capricious State action. 414 U.S. at 639-640 (1974).

Justice Stewart for the majority examined two explanations offered by the school authorities to justify their mandatory maternity leave rules — explanations also offered by the defendants in the present cases — and found them wanting; he concluded that the rules bore no rational relationship to the State interests urged in their support.

First, continuity of instruction of students was not furthered by prescribing firm dates for the teachers' quitting early in pregnancy. Indeed this policy could frustrate attainment of the claimed objective in many cases by needlessly causing the substitution of teachers in midsemester or near the end of a school year. The desired continuity could be adequately promoted by requiring the teacher to name, well in advance, a date certain for commencement of leave, and taking care to ensure availability of substitute teachers for emergencies. Second, the challenged rules were held to sweep too broadly in attempting to further a legitimate objective of keeping physically unfit teachers out of the classroom; here the rules went on a "conclusive" or "irrebuttable presumption of physical incompetency" at the fixed early stage of pregnancy that is neither "necessarily nor universally true." 414 U.S. at 644-646, 647-648 (1974). Due process required some "individualized determination" by competent medical judgment of the particular teacher's ability to continue to teach. 414 U.S. at 644. The administrative convenience that could be claimed for rules that avoided case-by-case determination was not weighty enough to validate an otherwise prejudicial scheme. The court, however, kept open the possibility that a rule terminating employment "at some firm date during the last few weeks of pregnancy" might be permissible. 414 U.S. at 647, n. 13 (1974).

The court also held that limiting a teacher's right to return to work until the beginning of the semester following the date on which her child was three months old (as in the Cleveland case) rested again on an "irrebuttable presumption" of disability that was unnecessary, arbitrary, and irrational and so in violation of due process. 414 U.S. at 649-650 (1974). On the other hand, disallowing return before the commencement of the semester following the birth and requiring a physician's certificate attesting to the teacher's health (as in the Chesterfield County case) were thought valid expedients — "narrowly drawn methods of protecting the school board's interest in teacher fitness" and "avoiding unnecessary changes in classroom personnel during any one school term." 414 U.S. at 648-649 (1974).

In a concurring opinion, Justice Powell skirted irrebuttable presumptions and employed equal protection analysis — "rational basis standards of equal protection review" — reaching thereby the conclusion that the school board had acted on classifications "either contraproductive or irrationally overinclusive." 414 U.S. at 651-657 (1974). Nearly all the opinions of State and lower Federal courts considering this question and finding similar rules unconstitutional are based at least in part on denial of equal protection.

Whichever may be the sounder ground of constitutional decision, there can now be little doubt that the rule of the Malden school committee must be held invalid at both ends — in its provision for mandatory "resignation" by the fourth month of pregnancy, and in its provision for a six-month waiting period after birth before reinstatement is possible.

Although the defendants' efforts to justify the terminations under the rule, as written, are now vain, we go on to consider whether the treatment actually accorded these plaintiffs was perchance compatible with constitutional standards. The plaintiffs in fact remained at work well along in their pregnancies until they decided for themselves that they could no longer continue, thus securing, after a fashion, "individualized determination." On the other hand, assuming that the letters of March 21, 1969, are to be read as a decision to enforce the rule at least as to reinstatement, rather than as absolute terminations, the plaintiffs faced at least a six-month waiting period, no less objectionable than the corresponding regulation struck down in the Cleveland case. The conciliation proposal of MCAD contemplated reinstatement by the September, 1969, opening of school, and the acceptance of the proposal by the committee could possibly be viewed as an equivalent "offer" to the plaintiffs. But although otherwise ready and willing to resume teaching at the opening of school in September (as they have stipulated), the plaintiffs balked at an offer that was conditioned on their accepting a retroactive six-month leave of absence from January 31, 1969, during which they would receive no sick pay and evidently could not accumulate further rights to paid sick leave. The school committee minutes indicate that even after March 10, 1969, the plaintiffs had from fifteen to twenty days of accumulated sick leave remaining to their credit.

The Supreme Court was not called on to say in the recent decisions whether a teacher absent from work because of pregnancy-related disabilities could be accorded diametrically different rights to sick pay than a teacher suffering from other temporary physical disability. But a classification such as that exemplified by the Malden sick leave rule appears arbitrary and unconstitutional, whether or not one relates it to discrimination based exclusively on sex, see Frontiero v. Richardson, 411 U.S. 677 (1973); Reed v. Reed, 404 U.S. 71 (1971); Stanley v. Illinois, 405 U.S. 645 (1972); cf. Green v. Waterford Bd. of Educ. 473 F.2d 629 (2d Cir. 1973); and especially is the classification invidious, since it burdens fundamental freedom of choice in marriage and family life. The Malden rule evidently applied to all illnesses or medical conditions causing absence from work — except pregnancy. The only justification suggested to us was that, with the means of family planning available today, pregnancy with its attendant infirmities is a condition "voluntarily" assumed, unlike ordinary sickness and injury which are said to be "involuntary." The distinction is shallow. We are not really helped by trying to classify pregnancy as "voluntary" or "involuntary." It is rather a natural incident of married life that definitely results in disability, but of variable duration. See Buckley v. Coyle Pub. Sch. Sys. 476 F.2d 92, 95 (10th Cir. 1973). In a sense, pregnancy is no more voluntary than disabilities incurred in the pursuit of nonessential activities with obvious risks of injury, such as playing games or even driving an automobile. Note, 7 Harv. Civ. Rts.-Civ. Lib. L. Rev. 260, 288 (1972). We are not to be understood as intimating that no State interests can ever conceivably be asserted to justify particular distinctions for purposes of sick leave between pregnancy and other disabilities. See Aiello v. Hansen, 359 F. Supp. 792 (N.D. Cal. 1973 — three-judge court). It is enough for this case to say that categorical disallowance of all sick pay for disabilities related to pregnancy was improper when sick leave was allowed for the other disabilities whether voluntary, predictable, normal, or unique. See Bravo v. Board of Educ. of Chicago, 345 F. Supp. 155, 159 (N.D. Ill. 1972). We note that the Equal Employment Opportunity Commission in its 1972 guidelines pursuant to Title VII of the Civil Rights Act of 1964, 42 U.S.C. § 2000e-2000e-15 (1970), stated not only that a mandatory leave or termination policy for pregnancy is considered prima facie invalid, but also that maternity leave must be treated like leave for any other temporary disability. 29 C.F.R. (1973) § 1604.10 (b). 37 Fed. Reg. 6837 (April 5, 1972). Since 1972, Title VII has applied to State agencies and educational institutions. Act of March 24, 1972, Pub. L. 92-261, 86 Stat. 103. See Wetzel v. Liberty Mut. Ins. Co. 372 F. Supp. 1146 (W.D. Pa. 1974). See also G.L.c. 149, § 105D, and c. 151B, § 4 (11A) (both added by St. 1972, c. 790, § 1, 2), and regulations on maternity leave and sex discrimination in employment promulgated by MCAD on May 24, 1973.

4. As the terminations were improper for the reasons discussed, the plaintiffs as tenured teachers are entitled to reinstatement with benefits. See Ransom v. Boston, 192 Mass. 299 (1906); S.C. 193 Mass. 537 (1907); S.C. 196 Mass. 248 (1907). Cf. Lowry v. Commissioner of Agriculture, 302 Mass. 111 (1939); G.L.c. 71, § 43A. But a question is raised about the plaintiffs' entitlement to back pay. The defendants invoke the usual doctrine of mitigation applicable to discharges under contracts for personal service: if the discharged employee could by reasonable efforts have disposed of his time by finding comparable employment, and thus reduced his loss, he will to that extent be denied a monetary recovery. See Clark v. General Cleaning Co. Inc. 345 Mass. 62, 65 (1962); Restatement: Contracts, § 336 (1932); Williston, Contracts (3d ed.) § 1353 (1968). In McKenna v. Commissioner of Mental Health, 347 Mass. 674, 677 (1964), the usual concepts were applied to public employees. However, the plaintiffs contend that tenured teachers are excepted by c. 71, § 43A, from the rule regarding mitigation. That section says that when the Superior Court on judicial review finds that a teacher has been improperly dismissed after a vote by a school committee pursuant to § 42, it shall reinstate the teacher "without loss of compensation". But § 43A, even if applicable through § 42, would not abolish the mitigation rule for teachers. After extensive discussion of history and policy, we held in Police Commr. of Boston v. Ciccolo, 356 Mass. 555 (1969), that a provision of the civil service laws similar to § 43A — G.L.c. 31, § 45, stating that an employee unlawfully discharged shall be reinstated in his office "without loss of compensation" — did not change the rule of McKenna v. Commissioner of Mental Health, supra, and we see no reason to construe § 43A differently. The case cited by the plaintiffs, McCartin v. School Comm. of Lowell, 322 Mass. 624 (1948), does not analyze the issue of mitigation, nor does Lucia v. Duggan, 303 F. Supp. 112 (D. Mass. 1969).

But having advanced to this point, the defendants are met with the proposition that the burden of proof is on them, as the parties responsible for the improper terminations, to show that the plaintiffs would in fact have secured similar employment and mitigated losses, had they made reasonable efforts. McKenna v. Commissioner of Mental Health, supra, at 677. Corbin, Contracts, § 1039 (1964). The defendants say that the plaintiffs could have returned to their jobs in the Malden system merely by joining with the school committee in accepting the investigating Commissioner's proposed terms of conciliation. But the refusal of the plaintiffs to do so does not satisfy the defendants' burden as to mitigation, even if the conciliation proposal is taken to be in effect an offer of reinstatement on the part of the defendants, for the proposal compromised the very constitutional right that the plaintiffs were and are asserting. See Williston, supra, § 1359, pp. 310-311 (1968); Corbin, supra, § 1043, pp. 274-275 (1964).

The record, however, shows plainly that under Malden's formal rule, the plaintiffs were entitled to apply for reinstatement six months after giving birth, with the chance, though not the certainty, of obtaining positions if not at that time, then eventually. The reinstatement provision was on its face unconstitutional, but it provided a means of mitigation, and it is not shown on this record that the defendants would have granted reinstatement under their rule only on the condition that the plaintiffs give up the remaining issues in their pending suit — a condition to which the plaintiffs would not be obliged to yield. This avenue of mitigation, presented by the record but not pursued below, should be explored on remand to the Superior Court. It implicates the further question, just when, having in view the plaintiffs' particular circumstances, the terms of the rule, and the situation within the school system, the plaintiffs could reasonably have been expected to apply for and secure reemployment in the Malden schools. The defendants would be responsible for back pay and related benefits up to the time of that putative reemployment, but not beyond. The burden, as we have indicated, will remain on the defendants.

5. In certain other particulars the cases likewise require remand for further proceedings to consider reduction of the defendants' liability for back pay. (a) Of course the plaintiffs should not be awarded damages in excess of the salaries they would have earned if they had not been improperly discharged. Louise Caroline Nursing Home, Inc. v. Dix Constr. Corp. 362 Mass. 306, 310-311 (1972). Ficara v. Belleau, 331 Mass. 80, 82 (1954). Williston, supra, § 1338 (1968). In the computation made in the court below, no deduction was made for the time the plaintiffs would have been absent from work because of pregnancy-connected disability beyond the period covered by their available accumulated sick leave. The record does not contain the data which would enable us to make this calculation for ourselves.

(b) In the case of the plaintiff Lane, there is a stipulation that if returned to the job she "would have continued teaching until January 1, 1971." There is some obscurity here. In her brief, Mrs. Lane suggests that she is not bound "by the hypothetical in paragraph 13 [the quoted stipulation]," while the defendants in their brief curiously do not refer to the stipulation at all. If the stipulation means that Mrs. Lane would in no event have taught past January 1, 1971, then she may not receive back salary for any subsequent period. This requires further examination.

The decree is vacated and the cases are remanded for further proceedings as indicated in this opinion.

So ordered.