Answer:
That it was successful in teaching people how to read and write. Education in the american colonies was deeply influence by protestanism, and the belief that people should be able to read the bible by themselves. Let's not forget that protestanism emphasized a personal relationship between the individual and God, and that the bible was the written word of God, and thus should be read by everyone.
Education was particularly good in New England, were in fact the first colleges in the United States were founded (Harvard College and The College of William and Mary).