MuseScore is an open source and free notation software available online. As of version 4, it comes with support for screen readers. However, MuseScore's support for JAWS is not currently as good as it is for Narrator or NVDA on Windows.
See MuseScore’s Accessibility Page for a guide to accessibility, focusing on navigation and usage with screen readers.
Using MuseScore files you can present score excerpts, musical examples, and even exercises to students via screen readers. You can create examples yourself in MuseScore, or provide previously created files such as MusicXML.
Students relying on screen readers can refer to the MuseScore Accessibility Page for guidance on Score Reading with a Screen Reader.
MuseScore’s functionality as notation/engraving software is fully accessible with the supported screen readers. Students relying on screen readers will be able to use MuseScore for composition elements as well as many theory assignments relying on note input (intervals, harmonization, counterpoint, etc.). For theory assignments, you may likely need to recreate or modify the assignments into MuseScore files if they are sourced from worksheets or other sources. (Be sure to privately hold these materials for screen reader users to request so as to maintain Copyright Compliance).
Students relying on screen readers can refer to the MuseScore Accessibility Page for guidance on Score Creation and Editing with a Screen Reader.