Originally Posted by riccil0ve
The only time I've ever heard of or seen someone fall off at the canter was when they were bareback, vaulting, or the horse skidded to a halt because the rider [me o_O] didn't turn at the corner. That was my first canter ever.
My point is, if a rider has complete control and is perfectly competent at the trot, they are ready for the canter. To be competent at the trot means they have a seat, and if they have a seat, they can canter. It's a different gait, and takes some getting used to, but they are ready for it. If a rider doesn't have a seat, they shouldn't be cantering.
A rider can have a good seat at the walk and trot. They have to develop a seat at the canter by practicing. You have to learn to sit a canter you just don't develop it without doing it.