In high school, whenever I study for an exam, I do not like to do math problems. I just study the concept, do a few examples, and go take the test.
But in college, what really motivated me to do more math problems was the fact that some of the questions in the exam can actually come out of those sample problems. Doing the problems in advance actually saves you precious time because you have already done the same problem before.
In order to motivate a high school student, you can offer incentives if they do all the problems correctly. If they find the curriculum boring, try to make it more interesting by applying the same problem in an everyday situation. Not only will it spark their interest, it will also help them remember the concept for exams.