Mass. Gen. Laws ch. 43 § 130
If a majority of the total number of votes cast at a regular city election for and against the adoption of a plan of city council organization or school committee organization proposed under section one hundred and twenty-nine shall be in favor of adoption of either or both such organizations, each such plan shall supersede the provisions of the city charter theretofore existing and of the general and special laws relating to such city and inconsistent with such plan or plans, but not, however, until the city council members or school committee members provided for in such plan, as the case may be, shall have been duly elected and their terms of office shall have begun. The said city council members or school committee members provided for under the plan so adopted shall be elected in accordance with the provisions of this chapter relating to such plan, and their terms of office shall begin at ten o'clock in the forenoon of the first Monday of January following their election. In those cities in which the mayor serves as an ex officio member of the school committee and which subsequently adopt a new plan of school committee organization under the provisions of these sections, the mayor shall continue to serve as an ex officio member of said school committee.
Mass. Gen. Laws ch. 43, § 130