Here's a question we were debating on my team. Assume a high school miler in good baseline shape, experienced, who is coming off a winter of just doing base miles but no workouts, intervals, tempo runs etc. He runs a mile at the start of the season, then starts the spring track season. Assuming no injuries and a good coach, how much could he improve by seasons end, after training? Let's assume his pre-training race was 4:20. Can he go 4:10? 4:05?