Mass. Gen. Laws ch. 31 § 61
Following his original appointment as a permanent full-time police officer or fire fighter in a city, or in a town where the civil service law and rules are applicable to such position, a person shall actually perform the duties of such position on a full-time basis for a probationary period of twelve months before he shall be considered a full-time tenured employee in such position, except as otherwise provided by civil service rule. The administrator, with the approval of the commission, may establish procedures to ensure the evaluation by appointing authorities, prior to the end of such probationary period, of the performance of persons appointed as regular police officers or fire fighters. Unless otherwise provided by civil service rule, and with appropriate adjustments to the timing of performance evaluations called for therein, the second paragraph of section 34 shall apply to persons covered by this section.
Mass. Gen. Laws ch. 31, § 31:61