Check out the May winning entries in the grade 3-5 level.
The Big Brick Banger
San Francisco, CA
I was dying for recess when finally, the bell rang! I shoved my book into my desk and ran outside with my class. Suddenly everyone stopped. Everybody started backing up. What was it??? Finally, I saw, and it was not a very good sight. It was a fat, gray gorilla swinging on our school's monkey bars!
My friends and I stood for about five minutes just staring at the fat, gray gorilla when I noticed that he was staring back at us. On his face was a look that he was hungry and that we were his enemies. Now, I didn't know if he was actually going to attack us, but I didn't want to take the risk. I needed to invent something fast!
I took a moment to think and came up with a quick invention that could save us. The invention worked like this: I would place the candy wrappers on the playground, just past the end of the monkey bars to attract the gorilla. Right at the end of the monkey bars I would hang the swing. Next to the swing, I would tie the scarf with the four bricks inside of it. The straws would be tied tightly in a bow on the scarf, keeping the bricks inside. One side of one of the straws would be tied onto the swing. The gorilla sees the shiny candy wrappers and swings over to them. The last swing that he grabs onto is the swing that is connected to the scarf. When the gorilla puts pressure on the swing, it makes the bow in the straws (that are connected to the swing) come lose which makes the bricks fall on the gorilla's head and knocks him out.
I used my invention and it worked! I saved everyone on the playground! (Later on I decided to call my invention The Big Brick Banger.)