Fourth grade twins Mitch and Amy fight a lot, but they stick together against the class bully. They even stick up for him in the end. 

Mitch learns reading is not as hard as he thought; Amy gets motivated to learn the multiplication tables; and in the end, they discover they can empathize with the bully. 

Cleary had twins herself, so I think she knows what she's writing about! Fun adventure for lower to middle grade children.