Middle school is not the time to engage in extreme training practices to improve your sprint speed. The risks are too high, and the stakes are far too low. Still, the performance of a middle school sprinter can affect opportunities in high school and chances for athletic scholarships to college. A program of moderately aggressive but relatively low-impact workouts can help develop the attributes a student needs without risking injury.
A sprint pyramid develops your ability to accelerate and recover from the effort of a sprint. Pyramid workouts consist of a series of sprint sessions requiring progressively lower effort. You can do a repetition-based pyramid, for example starting with five sprints, then four and so on. You can also do a distance-based pyramid, beginning with a 100-yard sprint and working your way down. The base distance of any sprint should derive from the distance of an athlete's regular event. For example, a 100-yard runner would do shorter and faster sprints than a 200-yard runner.
Interval training consists of alternating between periods of sprint-speed running and rest periods at a slow to moderate jog. Running intervals builds acceleration through practice while simultaneously improving your long-term cardiovascular endurance. An example of an interval workout for middle school sprinters would be to run 1 mile, consisting of 100-yard sprints followed by 200-yard jogs.
Running under conditions where it's harder to move your legs than under normal circumstances builds the muscles directly responsible for accelerating. One example of this kind of training is to sprint while wearing weights in a backpack or vest. Another is running in the shallow end of a pool. You can use your imagination to come up with other training challenge ideas, as long as they are safe and put extra load on your lower body.
Although high school and college sprinters use strength training to strengthen the muscles responsible for sprinting, this is contraindicated for middle school athletes. At that age, the heavy weights necessary to make a performance-relevant difference can overly stress the still-developing bones of a middle school student. For resistance training, sprinters this age instead should use challenge training methods or calisthenics.