Here's an error correction worksheet that elementary students typically do when studying comparative and superlative structures? This worksheet may help them to realise their mistakes in comparison sentences. It includes typical mistakes my elementary and pre-intermediate students do in my lessons.
The worksheet is cut into halves as G and S (to consolidate the pronunciation of G and S letters) worksheets. Just distribute the worksheets to pairs and then ask the pairs swap each other's worksheets to check. They learn more from correcting each other.