No person shall, within the hours of 6:00 p.m. until 6:00 a.m. enter
grounds of any public building of the City used and occupied for school purposes
for the purpose of loitering there or shall, within such hours, loiter or
remain upon such grounds or the sidewalks or steps of such building. This
provision shall not prohibit persons from entering school property for the
purposes permitted under MGL c. 71, § 71.