The question you need to ask is if he plans on continuing to train and develop after the season as well. If it is 16 weeks and then see you next year, I would train him differently than 16 weeks and then do cross country base in the summer. Either way the focus should be quality, not quantity, but if he will be a true distance runner later on, I would establish a bit of the more distance based routines including easy distance runs (not too long though), longer intervals, and doing a few mile races to work on strength. If it is a 400/800 guy and won't be used in cross, you have to attack the race as a sprint and extend the training up. If the kid can't run a 100 in under 15 seconds he will have a hard time being competitive as a 14 year old. Most competitive 14 year olds will run between 2:00-2:12 which is 15-16.5s per 100. You might as well not run that event if holding 15-16 second 100s is a struggle and might want to try the mile. Although, if it is a 400/800 runner I would suggest something like this:
Mon- Flying 30s. Around 6-8 with strong focus on form and max speed
Tue- Volume, something like 1000, 800, 600, 400. The need is to train the lactic system and build respectable aerobic endurance
Wed- Strides/strength
Thur- 6-8 by 200s or 300s at 4 seconds faster than current 800 pace. This works on decreasing the 400 time which affects the 800 directly. Long recoveries toward the end of the year, but this could easily be an intensive tempo at the beginning by doing the 200s at 800 race pace with 30-45 seconds recovery.
Fri- Strides/stretching
Sat- Race