Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 71, § 61

The school committees of two or more towns, each having a valuation less than two million five hundred thousand dollars, and having an aggregate maximum of seventy-five, and an aggregate minimum of twenty-five, schools, and the committees of four or more such towns, having said maximum but irrespective of said minimum, shall form a union for employing a superintendent of schools. A town whose valuation exceeds said amount may participate in such a union but otherwise subject to this section. Such a union shall not be dissolved except by vote of the school committees representing a majority of the participating towns with the consent of the department, nor by reason of any change in valuation or the number of schools.

A town may terminate its participation in a union by a majority vote of the school committee of the town; provided, however, that said termination shall only be for the purpose of forming an innovation school pursuant to section 92 or establishing different school governance structures. Termination shall be independent of any pending votes regarding dissolution of the union or pending votes by another town regarding its participation.