Here's a short quiz to revise comparatives and superlatives' spelling rules. It covers different spelling rules in a short set of ten questions. There are two versions in this PDF set: with QR code key and without QR code key. You can use the QR code version if you want to give this quiz as a homework assignment. It'll be much more convenient for giving students instant feedback. In the teacher's copy, there are also some feedback notes given for giving rationale of the spelling rules.
You can try out this material here.