To lose stomach fat, eat the right kind of carbohydrate like vegetables, whole grains and fruits. Train the body with strength training activities. You can walk or do some vigorous cardio activities at least five days a week. Get more tips at http://www.ehow.com/how_4425103_lose-stomach-fat.html.
I am concerned that an eight grader is worried about losing belly fat, first what is your current weight and if there is a true weight concern talk to your parents, teacher, or school nurse. These people see you all the time and they can give you the best advice on the best way to maintain your weight.
Eat less carbs and exercise. Allow yourself the amount of carbs that you can basically exercise off. It'll help if you know the amount of calories you're eating as well as the amount of calories you're burning off throughout the day. If counting calories really stresses you out, then don't do it, as stress may prompt your body to store more fat. You can simply eat in smaller portions. Focus on fat-burning exercises plus ab workout.