[geckoday]

It scans all options for the product and if it finds one with the name size it adds the text. So it works like you want it to. Tested and working fine for me.

Did you add it to the right .tpl? Sometimes I dig around in products.tpl for a while before I notice things don't look right and remember my site uses products_t.tpl.

Other than that I can only suggest some basic troubleshooting. Replace the whole smarty {foreach} stuff that was added with some plain text to be sure its in the right spot. If that's OK replace it with {$products[product].product_options|print_r} to see if you've got the [class] variable there. If that shows the proper [class] stuff, scratch head and post back.