School sport is wiping a few of our U16s out before training

For me, the important bit is to implement a traffic light system at the start of each session. Have the players self-assess their physical load as they walk onto the pitch. Those who have had a heavy school day sit out the high intensity, lung-busting conditioning blocks and focus instead on technical work, game understanding, or set-piece roles. It is a pragmatic way to keep them involved without risking burnout or injury. You are not diluting the session for the group, you are managing individual capacity within the same environment. If a player is truly wiped, their performance in high-speed transition work will be poor anyway, which creates bad habits for the whole squad. Let them drop into a shadow-play role during tactical drills or take charge of observing a specific teammate to provide feedback. At U16, they need to start learning how to communicate their own physical state to a coach, which is a vital skill if they want to progress to higher levels of the game.