Patience is a Virtue
If you get a bad vibe about the teacher from the start, or if your child seems to take an instant dislike to him or her, don't jump into action immediately. The beginning of the school year is a transitional time -- your kid just might need a little while to get used to a new teacher and a different classroom style, especially if he or she really loved the last teacher. Sit back and observe the situation before you decide to do anything about it. Things could work themselves out.
But if things don't improve, it's time to take an honest look at the situation -- and at yourself.