Education expenses: Where do I enter books & materials NOT paid to the school? It says I'll be prompted for that later, but I haven't been.

My child qualifies for the American Opportunity Credit and is currently at $2,123. The system questionnaire asked about books & materials bought from the school directly but told me I'd be able to enter the rest elsewhere. Where can I find that? All of her books were required by the school but had to be purchased elsewhere.