Hello! Below is a super fun web site to supplement any ruler lesson plan. My kids LOVED it! During indoor recess this is the game they requested to have on the promethean board, which I was more than happy to do for them! You can change the level of difficulty by switching what parts of the ruler you're working with. For primary grades you can have it be just whole inches or half inches, or for intermediate grades you can put it on sixteenth inches which are always super tricky to point out on rulers.
The Ruler Game