What to wear over a tank top dress?

I bought a dress that is one that looks like a skirt and a white wifebeater/tank top attached. the skirt is blue plaid (kind of pleated like school girl.. lol but it's not slutty (: ) but the tank top straps are too thin for my school dresscode, and i don't want to wear a sweater especially in summertime... could i wear a shirt over the tank top part or would that look silly? ideas? pictures? :) im not very fashion literate.. :P