This issue has been a real struggle for me to figure out; I am using Headway Theme, and it appears the theme is interfering with the ability for Woocommerce to display an 'Add to Cart' button for variable products.
I've tried multiple solutions from other online support forums and none have worked for me (yet). The moment I switch from default theme to Headway, the 'Add to Cart' button won't appear after selecting a size. It does not appear to be any of my plugins.
The store is http://www.prcclothing.com/shop. I don't have much experience at reading any page's code, so I don't even know what to look for.
Thank you for your help!