I’m a tense rider and have always had trouble getting my body to go along with the motion of the horse, especially my arms. I am petite and seem to have the most trouble with larger horses. I’m a rerider and have been back riding for about 5 years now. I ride twice a week in group h/j lessons and have had a couple of the newer school horses start bucking. Apparently it’s just me and no one else. Getting fast and bucking makes me more nervous and tense. The instructor says I need to work through it. I also tighten up on the inside rein especially when I get nervous. I thought for a while I was getting better and improving but I guess I’m not. I’m contemplating just quitting riding altogether because I’m so depressed. Maybe I’m just old and my body isn’t meant to do this anymore.
Sorry find a new place to learn. Newer lesson horses that are bucking is NOT your fault.
Safety first. Find a place with solid school horses or at least at this one do not ride the newer school horses.
It sounds like they are using students to train the horses. That is not how it should work in the beginning.
I agree that you need another instructor. You shouldn’t have to be training the school horses.
If you can find someplace that gives good longe seasons, or there position work, and can teach you how to fall, that will d a lot for your confidence and general ability.
You’re not too old and stiff. You just need to give yourself a chance.
Or at least position work 
Agree that you should be on lesson horses that don’t buck. However, I was also going to ask if you are doing any rider-specific fitness work off the horse? It can help a lot with confidence that you can stick with a spook or buck and keep riding forward. There is no shame in full seat silicone breeches either. I can recommend the Dressage Rider Training program (it’s not just for dressage riders). My confidence on my big greenie has improved a lot since I’ve been doing it because my seat is more secure and my balance is more solid. Make sure whatever you do incorporates balance as well as strength and stretching exercises.
You do not need to work through it. You need a different instructor who would not say such things.
And to be on a different horse, possibly on a lunge line with someone who knows how to give lunge lessons (like they do at the Spanish Riding School – check their instagram for some examples.). This can be very hard to find. I’ve found that instructors want you to progress! and do things!
Don’t burn any bridges, it’s entirely possible that this program will work for you later. But not right now.
I’ll second the Dressage Rider Training program, it’s all about strength and balance and being able to move each part of your body separately. Having this control over your body will give you confidence.
In the past I could make pretty much ANY horse misbehave. If I got scared I would tense up and take a death grip on their face. It took a reiner (Warwick Schiller) to finally convince me that the brakes are not in their face. So I’m sympathetic to your instructor saying “it’s just you!” For me it was. And no amount of my coach saying “LET GO” worked until I fixed what was going on inside my head.
Good luck, and keep us posted on what you decide to do next!
Curious where did he say the breaks were?
Fourth’ing the lunge lessons and exercises out of the saddle to strengthen your core and increase your flexibility. The lunging will help you work on your form without having to control the horse. Also, good lunge instructors will know mounted exercises to help you relax and gain confidence in the saddle.
Please don’t give up riding!! You can do this. 
For me, if an instructor can’t help me work through something with concrete strategies, they aren’t for me. It may be a problem I work on for weeks, or a natural “always” thing like how my hips are tight because of the way I sit at work, but they’ll always give me a way to work around it. Being told “work through it” by an instructor and that’s it, would have me quietly considering another program.
Don’t give up riding! I’ve been at it for a long time, and I still regularly have days where I get off and think…do I have any business getting back on again tomorrow? 
That’s riding! One day you’re feeling like you might go to the next Olympics, the very next you’re wondering if you’ve ever held reins before. Perpetual journey.
You can do stretching/loosening exercises just before getting on the horse. Centered Riding has a series that really helped me, as I tend to be tense and anxious. Very comfortable and secure on a horse, but still habitually tense.
These days, I do yoga and meditation, which have a semi-permanent relaxation effect on both body and mind. The yoga, in particular, really helps with my back. I didn’t realize how tight it was until it wasn’t any more.
If you do decide to switch barns, you might even consider changing to western or dressage. It can feel a lot more secure riding with a longer stirrup and bum firmly down on the deeper saddle. Western horses also tend to be smaller.
Good advice. Then when you get better instruction
… SING. It will use your focus so your body can relax.
Part ways with your instructor or be real clear in your communication on what you want, she likely doesn’t understand the struggles of a desk jockey warrior getting back into riding.
Everything in your body is probably tight and being put on inappropriate horses is not helping you. Yoga, stretching, and practicing relaxing your muscles off a horse, then practice at the walk, etc.
Be real with your instructor on what you want, a solid, safe lesson horse that is a true confidence builder and you can have fun with. Adult re-riders don’t necessarily want to be challenged with learning to ride a greenie but want to have a fun, relaxing couple hours enjoying our hobby. Some re-riders are game to ride all the greenies and get back where they were before. Different people, different goals.
I’m a mid 40’s re-rider with two horses at home that still lessons at least once a week for that fun hour where I can focus on me.
This is something you have to work through. You’ve been back riding for five years, it isn’t like you just started back a few months ago. Most of it is probably mental. Sorry.
Have you had any falls or injuries? Do you have anyone at home harping on you “not to get hurt” or “don’t fall off?” “You can’t afford time off work” Hearing that all the time can kill your confidence. Ask me how I know. At some point, I must have told Mom to can it, but I don’t recall when.
If you aren’t comfortable riding big horses, ride smaller ones. Tell your instructor you want a smaller one. You are a customer in this barn; if you don’t like riding big horses, don’t. It’s OK to tell a trainer you are not riding anything over 16h.
You’ve gotten some good responses but…
Learn to relax in the saddle. Tell your instructor you need to relax in the saddle.
When you get in the saddle, do a head to toe survey of your tension and relax those tense muscles. Take your time here. Really make sure you are relaxing those muscles. You’re on school horses, they get it and read the rider like a book. Stand up and stretch those leg muscles so your toes are the highest point of your calf. Take this time to transition from work/home life into riding life. You aren’t alone in this.
The instructor shouldn’t be telling you to “work through it”. The instructor should be telling you HOW to work through it, if anything. Heck, so many ride horses for enjoyment. You deserve to ride horses who are fun to ride and can teach you things, and minimally react to your reactions. THAT is a school horse who can get you to gain confidence in your own abilities. Please consider a different riding program before giving up on riding. It doesn’t sound like this is a good riding program.
Two things:
One- can you take some private lessons? Working through issues with confidence and tension can be very difficult in group lessons. Your trainer’s attention is divided, and he/she not always watching you, so things get missed. Even if you can do one private and one group lesson a week, this would be preferable. You need some one-on-one coaching to identify specifics that will help you relax, soften your arms, and create a list of tools you can use to help quiet and comfort the horse.
Two- as hard as it is, try not to get discouraged. We all oscillate between thinking we can ride, and thinking we suck! I expect that your trainer is putting you on more challenging horses because they believe you are ready and they want to expand your skill set. If you aren’t interested in this, you should have a frank conversation with them, and potentially work on finding a new trainer. I would encourage you to be open to a discussion, though, about why they want you riding these horses, and what they are hoping you will learn. I have students who want to continue to advance and to learn to ride harder horses, and I have others who are happy with riding the easy ones and just want to enjoy the ride, without really working towards any goals. Both are fine! However, you need to make this clear with your instructor, and make sure their teaching style is compatible with what you want out of the ride.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This!
Your post resonated with me, because I rode at a lesson barn factory for years, being told “the horses only do x with you.” However, looking back, many of the horses were only questionably trained and had soundness issues, and quite a few of the other riders I spoke to who rode the horses in other lessons had the same problems. So sometimes it’s an instructor just not having the time or knowledge to offer constructive advice. Of course, some horse-rider combinations are problematic, and a better rider will get a better ride (most of the time) out of a school horse. But it’s not helpful advice and may not necessarily be 100% objective advice. The fact that it’s just the newer horses that are bucking might be due to the fact the horses aren’t really tuned up for the program yet.
I would agree with the suggestion to try a different discipline (dressage, IMHO) and get private lessons. Hunter-jumper barn group lessons, especially if everyone rides on the flat together, can be very difficult because you’re not only dealing with your own issues and that of a school horse’s, but also the issues of everyone else in the lesson and their horses.
Time to go trainer shopping.
I’ve been teaching for thirty years, and telling a rider to “work through it” when they are riding in fear is TERRIBLE TEACHING. She is not giving you tools to do so.
Find someone who will put you on the longe line and help you find your balance. Only then can you expect your body to relax. I recommend a dressage trainer, even if you ultimately transition back to HJ.
YOU SHOULDN’T HAVE TO TELL YOUR INSTRUCTOR THAT YOU NEED TO RELAX IN THE SADDLE. It’s her job to assess and address that. I think you are in a group-lesson program, and as such are very low on the food chain in a HJ barn, especially if you are not on “the future-owner or lessor” track. Find a smaller, more personal barn and get private lessons.
There are things a coach cannot see and things they can. When my horse does something well, my coach notes it and asks me ‘what did you do there’ and i have to stop and think…what DID i do? lol. A lot of times it’s no rein/leg/butt anything but just relaxing and revisiting my breathing. (‘yoga breathing’ inhale deeply, …like through mouth, exhale slowly through nose). I find that when my breathing is deep and full my body relaxes and my horse relaxes too.
