Idaho Code § 33-201
The services of the public schools of this state are extended to any acceptable person of school age. "School age" is defined as including all persons resident of the state, between the ages of five (5) and twenty-one (21) years. For the purposes of this section, the age of five (5) years shall be attained when the fifth anniversary of birth occurs on or before the first day of September of the school year in which the child is to enroll in kindergarten. For a child enrolling in the first grade, the age of six (6) years must be reached on or before the first day of September of the school year in which the child is to enroll. Any child of the age of five (5) years who has completed a private or public out-of-state kindergarten for the required four hundred fifty (450) hours but has not reached the "school age" requirement in Idaho shall be allowed to enter the first grade.
For resident children with disabilities who qualify for special education and related services under the federal individuals with disabilities education act (IDEA) and subsequent amendments thereto, and applicable state and federal regulations, "school age" shall begin at the attainment of age three (3) and shall continue through the semester of school in which the student attains the age of twenty-one (21) years.
Idaho Code § 33-201