Mass. Gen. Laws ch. 71 § 21
Every town which has accepted chapter three hundred and eleven of the General Acts of nineteen hundred and nineteen, and in which, in any year, two hundred or more minors under sixteen are employed not less than six hours per day by authority of employment permits described in section one of chapter one hundred and forty-nine or home permits described in section one of chapter seventy-six, exclusive of minors employed only during vacations, shall, except as otherwise provided in this section, and any other town which has accepted said chapter three hundred and eleven, may, through its school committee, local board of trustees for vocational education, or both, establish at the beginning of the next school year and maintain continuation schools or courses of instruction for the education of such minors, and for such others as may be required to attend under section twenty-five. The said schools or courses shall be in session the same number of weeks in each year as the local high schools, and the sessions shall be between the hours of eight in the morning and five in the afternoon of any working days except Saturday. If in a town required to establish continuation schools or courses under this section, after examination of the records required to be kept under sections eighty-six and eighty-nine of chapter one hundred and forty-nine, it appears that in each of two consecutive years the number of employed minors described above falls below two hundred, the school committee of said town may apply to the department for exemption from the provisions of this section, and, if specifically exempted by the department under conditions defined by it, said town shall be deemed to have come under the permissive provisions of this section and shall so remain until two hundred or more such minors in any year are employed therein.
Mass. Gen. Laws ch. 71, § 21