Make variant fields not required

Site URL: http://www.wordplaywriting.co

I sell seats in classes on my site. I'd like to have one drop down for classes that are being offered as an 8 week term, and another for classes being offered as a 12 week term. Right now, the only option is putting "12 week term" in the variant's description, which makes things pretty clunky and long-winded. I'm happy to use a separate plugin for this, but don't see anything that will do the trick.