Sub post-types of custom post-type
I am working on a site for a non-profit that offers foreign language classes. I am looking to use custom post types. Two custom post types relevant to this question are "Classes" and "Class post". Multiple "Class post" posts will reference a unique "Class" ID/name. I will most likely use the posts-to-posts plug-in for this purpose, although I am also looking at something called pods framework. In any case, I wish to have sub post-types (homework, resources, class material, etc.) of the "Class post" custom post type. Just like how the native WordPress post type has sub-types of aside, link, video, audio, etc. How would I accomplish this? Is custom taxonomy the way to go? Some pointers will be appreciated.