PETS! by Melanie Godsey:

It’s a tail-wagging time at Pet School, where Biscuit the pup and all their furry and feathered friends learn to sit, stay, and help a human in need. When things get ruff for Biscuit’s best human friend, Corey, it’s time to fetch help. A once-close friendship has gone to the dogs, and the bus stop becomes a bullying zone. Using every paws-itively clever trick from Pet School, Biscuit will stop at nothing to help Corey and teach the other kids that being an upstander is the best trick of all.