Speaking in general terms and experience, most HS/college MALE athletes tend to try to do all their training on their own / with their buddies at the local gym.
To be fair, MOST can probably do a decent job on their own getting stronger and packing on size if that is their goal, especially if they have a decent training age.
However, FEW do a good job solo of training for speed, power, agility, acceleration, mobility, etc… even putting together a well balanced program.
The best thing you can do if you have the means is to DROP your ego and work with a coach, even if just for a few days per wk!