Change the table of contents so that you see the chapters first and can then open a chapter to see the subchapter.

[barbarer]

My students find it difficult to navigate the table of contents since it is so long and always displays all subchapters.

They would like to see all the chapters initially and then have the ability to drill down to the subchapters by collapsing menus or expanding them.

[bnmnetp]

You can accomplish this today by changing the :maxdepth: parameter on the .. toctree:: directive in your index.rst file.

Collapsing menus are cool, but they are not built in to sphinx and will take time and effort to implement. Maybe a nice student project.