From DESE, the Department of Elementary and Seconday Education:

What is a school council?
A school council is a representative, school building-based committee composed of the principal, parents, teachers, community members and, at the secondary level, students, required to be established by each school pursuant to Massachusetts General Laws Chapter 71, Section 59C.

What is the reason the Education Reform Act calls for establishing school councils?
Teachers, parents, and community members can become more committed to improving the schools and more supportive of the public school system when they enjoy the opportunity to serve or be represented on a school council that has a role in shaping the policies and programs of the school. One Massachusetts school system, which instituted site-based decision making and school councils prior to the statewide mandate, includes the following preamble in its guidelines for councils:
Values behind site-based decision making through councils: [the council] improves student outcomes by uniting, in responsible participation, those closest to the teaching-learning relationship; [the council] creates through the development of a shared vision and planning a school environment which unites all members of the school community in a sense of belonging, commitment and growth.