As a former middle school and high school teacher, I will tell you this, YOU CHILDREN ARE REWARDED EVERYDAY for things you may think they should not be rewarded for. We all strive off of motivation. I am sure your children's teachers give them all types of rewards, homework passes, extra recess, pizza parties, candy, and the list goes on and on. The principal gives parties to entire classes or groups of students for whatever reason. So if you are a child you have to think, I get rewarded at school for my great performance but not at home "what is going on?, why should I continue to work hard for nothing?"
REWARD your children. My mother was a school teacher, and I was rewarded. But i will have to say I was rewarding for LEARNING and DEVELOPING SKILLS instead of for my grades. The grades do not mean squat if you cannot think, comprehend, and create. Anyway, i getting off on a tangent.
What my parents told me was "SCHOOL IS YOUR JOB, and we will pay you for doing well." I learned all about performance evaluations, and saving money and investing in money because of this.
it is a new time and a new day, remember school is a full time job and children should get rewarded, what ever system you set up for them make it rewarding to them. Ask your children what type of reward they would like, and then let them come up with the performance standards, you may be surprised how tough they will be.
if you went to work and did not get any praise or raise or other reward, you would probably quit, and that is what your children feel like doing.