One detail that matters given what you sell, since it is easy to read the condition more strictly than it is written.
The waiver condition is about what you distribute on the App Store, not about whether your organization has revenue. It applies as long as you distribute only free apps, with no paid apps and no in-app purchases.
Selling physical books and classroom items is not in-app purchase territory to begin with. Apple's guidelines require goods and services that are used outside of the app to be purchased by means other than in-app purchase, so taking payment for physical items through your own payment flow is not offering IAP and does not conflict with the waiver condition.
Where it would conflict is digital content consumed inside the app: an e-book readable in your app, a paid course, a subscription. Those are in-app purchase, and that is what removes eligibility.
One more thing worth checking before you plan around it. The waiver is available to organizations, not individuals, so the enrollment itself has to be the organization type. That brings the organization requirements with it: a D-U-N-S Number, a publicly available website whose domain is associated with your nonprofit, and a work email address on that same domain. If the 501(c)(3) ends up enrolled as an individual, the waiver is not available at all.
Topic:
Business & Education
SubTopic:
General