My biggest advice for you and what someone has mentioned already is time to let the brain make the connections.
Explain something, get the try or a semblance of what your asking and release all pressure. If your on board this means walk breaks, relax contact, stay quiet for a couple minutes or let him quit if he was having a hard time and finally got it. I had a day where my youngster was spooking with the other horses in the arena and snow sliding off the roof. I went back to basics and as soon as he relaxed for a half lap which I was asking him to do, I halted and jumped off, let the girth out. That’s a huge reward. Less is more, honestly.
An old trainer once explained the neurological side of how horses learn at differing ages. It seriously is true. I can’t remember the exact times but it was similar to this, give or take.
A 2y/o will take 2 days (roughly) to generate a new brain connection and commit the task you were teaching to memory. Essentially the ‘ah-hah’ moment. 3 y/o roughly 36 hours, 4 y/o 24hours and gradually decrease .
So, give a younger horse more time to think/time off after teaching something.
Good luck! OTTBs are so rewarding