Most kids with ADHD have problems at school. One of the best things you can do is to use an assignment notebook. Write down all of your homework and be sure to check it off as soon as you are done. Also, put your homework into your bookbag right away so you will not go searching for it the next morning. If you get squirmy in class, ask your teacher if you can hold something soft and squishy to play with.
Some kids find it is easier to pay attention if they have something to do with their hands.
Ask your parents to make a calendar at home and hang it on the wall. Put any tests, or important dates on the calendar. Ask them to remind you to check it each day. Your parents can ask your school to test you and see if they can give you some extra help. This might mean having a tutor come to your classroom to help you get organized.