Without a doubt were Cammie's Choice, Cammie's Challange and Cammie's Cousin.
Cammie was an awkward teenage girl who wanted to learn to ride. She was befriended by a local trainer and learned to take care of horses from mucking the stall to riding champion hunters.
I checked out these books several times a year for all three years that I was a student at Central Junior High School. I lived every moment of them over and over.
It probably had a lot to do with my success as a greyhound trainer.