How do you get the girls to move on big nate island?

The girls are at recess (a very long one, obviously) and will only leave if the school bell rings. Unfortunately, the bell is broken and there is a seagull guarding it. You will have to repair the bell. (The clapper is hidden away.)

You will have to do the following :

1. Recover the school bell clapper (in the secret room below the detention room)
2. Get the lobster from the sunken trap past the lighthouse
3. Scare away the seagull from the bell tower (by turning the lighthouse light to the left with the lobster)
4. Climb the tower and ring the bell.

(see the related question)