I always tried to vary my lessons. I was working with no lead rein, but it might help
The elements of every lesson were essentially:
* balancing exercises
* figure eights
* going through cones
* posting
Aside from requiring that they do the balancing exercises before posting, I would let them choose what order to do this in. It made them very happy, and they felt like they were getting variety. I also would pick a topic to explain to the students while they were practicing, like "Horses eat grass in the wild, and they eat it all the time. They eat even when they're snoozing. They only really sleep about 2 hours every night, can you believe it? They can eat and snooze, which is why so many people think horses sleep standing up. But they do lie down when they really sleep; it's very cute" etc etc.
I'll talk about anything I think they can grasp, as long as I explain it--like "horse's hooves are really just very strong fingernails and they have to be trimmed regularly," or "lessons shoud be fun for the horse too, so let's make sure we reward him for being good and give him a carrot when we get in," or "The reins are attached to a metal thing in the pony's mouth. It's called a bit. When we use the reins we want to be very gentle; think what having a metal thing in your mouth would feel like" andso on.
A lot of times my lesson topics were related to the lesson at hand. For example, every so often I would let them ride bareback. "Why do we ride? Because it's fun. Why do we ride bareback? Because it's fun! It also helps us really really feel what the horse is doing. Feel the back moving?" etc etc
I explain posting trot every time--kids that age don't really retain it, but it helps them to perform better. (What is trot like? Is it smooth? Nooo, it's bouncy. What happens if we sit still? We bounce! So what do we want to do? We want to bounce without hurting our backsides or the pony's back. That's posting.) When they do start to remember from lesson to lesson, it makes them happy. I usually give them an opportunity to tell me something I've already explained, and then explain it if they don't remember.
I also review the lesson at the end: "What did we do today?" A lot of times, what I'll get is "we took off the saddle and we gave her treats." I have to probe to get any further back, and to remind them of what we did toward the beginning of the lesson. I do think it helps them remember, to remind them at the end of what we did.
So, even though what they're doing is repetitive, they feel like it's different because they get to choose which to do first, and also while they're practicing they still get to talk (learn!) about horses.