From Hammond, referring to the second half of the 5th Century B.C.:
All citizens were literate, whether they learnt at home or at a private school, but only the well-to-do could afford the higher education given by the sophists. Yet all citizens were exposed to new ideas. They heard them in the plays of a Euripides, in the pleadings of an Antiphon, or in the oratory of a Georgias, and they discussed them with quick-witted avidity in the crowded city. In answer to an increasing demand there was a rapid expansion of the trade in books, and in 405 Aristophanes assumed that his audience knew the latest fashionable treatise. Their power of memory too were highly developed by judging plays, politicians, or prisoners at a single hearing.