You are supposed to use small shells. I used the large ones this time and they got really big and started to fall apart. If that's all you have, don't make a special trip to the store. Just boil them a little less than called for. The small ones seem to work so much better for some reason.
This makes a ton, so be prepared for leftovers! Or you can always half the recipe.
1 lb. box small Shell macaroni
24 oz. mozzarella cheese, grated
48 oz jar spaghetti sauce
16 oz. can tomatoes
2 lbs. ground beef
Cook shells to al dente according to package instructions. Brown hamburger. Throw all ingredients into a crock pot and cook on low for 4 hours.