When agreeing to HBO Terms of Use upon account creation, it states "You may not copy, reproduce, distribute, publish, enter into a database, display, perform, modify, create derivative works, transmit, or in any way exploit any part of this Service, except that you may access and display material and all other content displayed on this Service for non-commercial, personal, entertainment use on a single computer or device only."
HBO has not made provisions for educational screenings of it's content through personal accounts. While classroom use would be non-commercial, it would not be considered personal use. Streaming HBO content in a classroom setting would be a direct violation of licensing terms (section 6a)