I am a freshman in high school and ran the 200 and 400 in junior high. I ran cross country during the fall but wasn't very good. Over the winter I got better and I am now 2nd or 3rd on the team (1st guy on the team is a mid 4:30s and 9:55 guy) during our winter Saturday runs. My coach says that if i move up to the mile or half mile like I want to it will be harder to get faster so I need to stay with the 400 and 200 to maximize my speed before moving up. He says overall it will be better for my longer distances. My question is if I move up, will I not be able to work on my top speed, or if i stay at 400m, will it have a long lasting effect on my speed and help me with the mile and half mile distances? I love to run longer but if It will help my kick or 800 speed then i will do what he tells me. What do you think, does his claim have any truth to it?