Wow, do you live in germany and ride a lesson horse named otto
Seriously though, I had a lesson horse exactly like that.
How old is the horse?
How many times a week is he ridden?
Is he ridden by young children (<12)?
Oh, and do you ride english or western?
Mostly my advice is to stick with it! Otto was a total brat when I started riding him, and while his brattiness is still present, he has come to respect me more, especially with grooming! (man that horse is a brat :P) But, I love him, and can't help it.