Alison Lester 
Circus Horse 
Horse Crazy Book 2

In the second volume of this charming series, friends Bonnie and Sam are determined to win the local talent contest. And they know that learning to do trick riding on horseback will secure victory. When the girls pick a real-live horse to practice on, all bets are off. The excitement will keep young readers turning pages, as Bonnie and Sam discover that some things are even better than winning.