"It is entirely possible that Shakespeare's wife never read a word that he wrote," Stephen Greenblatt tells us in Will in the World. It is also possible, given the absolute absence of evidence to the contrary, that Ann Hathaway was blind. She may have been illiterate when Shakespeare met her, and he may have spent happy hours teaching her to read. [...]This could also be seen as "evidence" in favor of Shakespeare himself writing all of this plays, as the issue of his wife and children's illiteracy is an argument sometimes used against this position.
It is more likely, however, that long before she became intimate with Will Shakespeare, Ann's Puritan family had made sure that she could read. By the 1580s, people who couldn't read were sensible of a spiritual as well as a social disadvantage, because they were barred from direct access to the word of God. In the winter, when there was little or no work for children in the fields, even the humblest farming villages set up dame schools, where girls were taught to read and sew, boys to read, write and cast accounts. Reading was essential if a woman was to follow her daily devotions; sewing provided for her and her family. In Shakespeare's plays we encounter men who cannot read, but never women.
(via Sarah Weinman)