Now that I've actually googled it, the evidence for Blackbeard's literacy is very, very weak. A few fragments of the 1712 edition of Cooke's "A Voyage to the South Seas" were discovered in the breach of a cannon on the wreck of the Queen Anne's Revenge. They had been used as wadding, which doesn't suggest great reverence for books. Although presumably this happened at Ocracoke so it may just have been desperation. There's an article here.

Apparently some documents have been found pertaining to an Edward Thache who may have been Blackbeard. If it is him, he was literate and had an elevated social origin. Article here

For the show, my head canon is that Stede will definitely teach Edward to read and write!