The year, by the way, was 1647. Here is the act, as best I could find it (most of the websites which carry the information just summarize it for their particular agenda)
"It being one chiefe project of that old deluder, Satan, to keepe men from the knowledge of the scriptures, as in former time .... It is therefore ordered .... [that] after the Lord hath increased [the settlement] to the number of fifty howshoulders, [they] shall forthwith appoint one within theire towne, to teach all such children as shall resorte to him, to write and read ... and it is further ordered, That where any towne shall increase to the number of one hundred families or howshoulders, they shall sett up a grammar schoole for the university."