Problem with the WHOA button, please help!

At my riding school there is this one horse that I ride and I absolutely adore him but the only problem is sometimes he has a little problem with slowing down!

The other day in my lesson we do things such as going from extended canter on the long side of the arena to collective canter on the shorter side of the arena to start training him to slow down on demand... He was doing this sooo well; the problem came in when we were jumping

Over single jumps he would be fine and just speed up a little before and after the jump but then slow down again when i half halt but over sets of jumps such as triplets? three jumps in a row ( sorry for my terminology, still learning so someone can correct if wrong thanks ) he would go over the first one and then he would go into an extended canter and I would try half halt but he just won't slow down and instead speeds up, then he kept ducking out to the right of the third one! Problem is which didn't help the situation and probably made him stress is that i started getting nervous and every time he speeds up i tend to lose my position and obviously then lose control. I tried to sqeeze a little with my right leg and half halt with my left hand but he was still ducking out and not slowing down :(... We finally stopped him ducking out but that was with the help of putting poles on the right side of the jump

Can anyone give advice on what was happening and how to solve it and possibly how to strengthen my position such as exercises i can do ect? My teacher is brilliant and knows what to do but sometimes it's nice to hear other peoples opinions and advice on what to do?

thanks

What I would do is set those 3 jumps far enough ahead of one another so that you can come into the first one, and halt before the second one. Pick up trot, trot the second, then halt before the third one. It might not be pretty, but you have to get the job done so your horse believes in your request. Once it gets to not be such a struggle, you can trot in, maintain trot, and trot the entire thing. If he goes to canter and you ask for him to trot and he doesn't, halt him. Sit back,and halt him. Repeat until he can maintain a trot through the 3 jumps. Next you'd canter in, trot the second, canter out. Keep mixing it up.
Anyttime you feel like you'd want to slow down but he doesn't, slow to the next gait. It's more extreme than just slowing within the gait, sometimes you have to break the gait to get the response you're looking for. Soon enough he will learn that surging off on his own agenda isn't the plan and he will wait for you. :)
When you are doing the exersize of trotting the 1st, halt, trotting the 2nd, halt, turn him left and do not jump the 3rd. Take away the poles from the jump, and intentionally turn him left and forget about the 3rd jump. Do that until you do not feel him want to shift right from underneath you. From there you can start to add in the 3rd jump, but jump it on the left side. Have a plan, and committ to it. Know you can make it look pretty later. :)
Good luck

If at any time you feel him start to get hyped up put him on a circle right away. Keep him there until his paces is steady and he is relaxed. The consistancy of the circle will help him calm down. The more hyped up he is, the smaller the circle.

Wow thanks for the detailed response koomy56 :) it all sounds promising and im sure i will see a difference so will definitely try that out the next few times I ride him :)

Thanks Spirithorse, I usually do circles when he is hyped up but never knew to make the circles smaller the more hyped up he is so will also give that a try out :)

Well will be going riding with him next week tuesday and thursday so hopefully will get to see how he reponds and give you an update on it :)

Thanks again!

I would be prepared to try each/all of the good suggestions you have received, e.g. halting, smaller circles, slowing to the next gait, etc. In my experience, one of these will work better (or faster) than the others depending on the horse. Our 6 yr old mare would make doing even tight circles seem like a test of wills (or perhaps a game), but breaking the gait worked very well.
Good luck.