Beth 2 - *I* control the tempo and rhythm!

I had a lot more questions for Beth today, and Charlie was not at his best.  He was a little stiff and sore from yesterday, and because we rode with George, he was way more interested in where George was and what he was doing than what I was asking him to do.  He got back in the trailer and proceeded to paw it for like 30 minutes - very annoying.
We started with how you halt by softening your legs.  The trick is to soften your butt and legs.  I've been driving forward with my butt while softening my legs, but the halt needs to come from the lower belly instead.  This same place is the center of all activity - before every request (an up transition, a down transition), breathe into the belly and then think about it.  So if I am asking him to pick it up a bit, I use my leg, but I keep the impulsion from just going out his nose by stopping it with my core - not my hands.
This, I think, is the piece I'm having a hard time wrapping my head around.  It is something I rarely use, but once it's operating, it makes everything else so much easier.
So for a down transition from the canter, I use the core and the outside rein and then use the core again to keep the trot speed the same as the canter, just a different rhythm.
We worked on trot circles one direction, then changing through the center to the other direction.  Each time we'd change direction, I'd throw everything away, so Charlie would rush off onto the forehand at the start of the next circle and it would take me a whole circle to get it back.
I'm not sure why I'm doing that, but it was good to know once I figured it out.  It goes back to riding every step.
The other big issue was the same as what Major Beale has said - being an interactive rider instead of a reactive rider (with the following step being a proactive rider).  I can control how big the trot is by how big my seat is - I don't have to let Charlie choose.  Because Charlie was pissy today, this actually gave Beth an opportunity to have me redirect it instead of just going along for the ride.  As annoyed as I was (and as useful as it was to know he's better alone), that was worth it.
All gaits down transition is through the core, which also controls tempo and rhythm.   But an up transition needs leg first, but then you have to channel the energy.
This sounds so - hang on, let me go get my magic crystals - but it made sense while I was riding it.  But it is a slippery one - not quite fully within my grasp yet.
I think I said this yesterday too, but the other important part is to do well what I can do, and once I've mastered that, ask for more - just like the stages of dressage tests go.  Just because I want to be doing a stretchy trot circle doesn't mean that Charlie can zing along in a stretchy trot circle the first time I ask for one, especially after several years of not doing it.
It was another great lesson, and it was fun to go with Julie and have company on the drive.
I watched Julie's lesson (while Charlie was kicking the trailer) and it was really, really helpful.  Julie was nagging George for more canter because he was being slow, and she is a much better rider than me, so it was really helpful to watch someone better than me have a problem I have too.  There is something about not trying to ride at the same time, but being able to watch the cause and effect and the instructor's words that really helps me get some of the concepts.  It also helped because Julie would ask clarifying questions, so I could see where she was struggling with how to implement the instructions.  George responded a little differently than Charlie might, but it was still really interesting to watch.