If you use a Google Site with your class (or as an eportfolio option), you can choose to have an announcements-style page, which functions similarly to a blog and has a built-in RSS  Subscribe to posts link.

But never fear; there are other ways to incorporate subscription options to allow access to more visitors! note: if you are creating a site through a Google Apps for Education or Business domain, your domain must have Feedburner enabled in order for this to work.