Unfortunately the "sticker" issue is something that will likely be a part of your life for many years to come. It sounds like your son is bright, curious and energetic. Everything that a little boy should be. It is natural for him to "test" new behaviors.
That said, if the behaviors he is exhibiting at preschool are not terrible, let the teacher hold him accountable. All children are going to slip up every now again--especially when they are pre-school age. If he is not hitting, biting or creating a huge distraction all of the time, it's probably normal little boy behavior.
Reward the positive so that he begins to see that there are both good and bad consequences for behavior. Establish your own sticker chart at home, and be sure to include little things so that he is sure to be successful. Keep it positive.
Stay in close contact with the teacher, and try to determine if the other children are also being reprimanded. Too often, teachers tend to be harder on those who are typically well-behaved to "set an example" for the other little ones.
Although I am an advocate of addressing anything that happens at school with reinforcement at home, I also believe that the if you dwell too much on the negative, you run the risk of hurting self-esteem and inadvertently create new negative behaviors.
There is a reason that schools have age recommendations for beginning kindergarten, and many teachers will tell you that with all the new requirements for the first year of school that age should actually increase to six rather than five.
Four year olds need to run around and learn through their play--not be forced to sit still for long periods of time. They need to be creative and color outside the lines. There will be plenty of time to learn to read and write sitting behind a desk. But there is only one chance to be four--to explore all of the new things you see in the world by touching and smelling and yes, even tasting them.
Try not to look too far down the road. Enjoy your four year old now. Chances are he will settle down and be a wonderful student. He should think of school and learning as fun. His teachers should cultivate that creativity and natural desire to learn.
My youngest daughter is 7, and her second grade teacher lets her do her math under a table in a corner of the classroom. It sounds silly, but she loves it. It's her own little corner of the world and she feels secure and comfortable there--inevitably she scores very high on her tests. She is doing her own thing--and what the teacher wants all at the same time! It's a good lesson in control.
Many teachers are resorting to taking time off of PE or limiting recess as a discipline tactic for rowdy youngsters. When my son would get too active and rough, I actually required him to run laps around the house to burn off the energy. Or came up with some other creative activity. It worked wonders!
Good luck. Be Creative.
Read Harold and the Purple Crayon!
Enjoy being four--together!