Although it dates to the second century, Lucian’s mockery of the Christians through the figure of Peregrinus certainly has some bearing on literacy at that time:
καὶ τί γάρ; ἐν βραχεῖ παῖδας αὐτοὺς ἀπέφηνε, προφήτης καὶ θιασάρχης καὶ ξυναγωγεὺς καὶ πάντα μόνος αὐτὸς ὤν, καὶ τῶν βίβλων τὰς μὲν ἐξηγεῖτο καὶ διεσάφει, πολλὰς δὲ αὐτὸς καὶ συνέγραφεν… (Luc.Per. 11)