I feel like by the time you get to high school, particularly juniors and seniors, it becomes too late to reach a lot of kids. They're either going to wind up failures or they're already on track to succeeding. Not much of a difference I can make.
At least in middle school, it's a transition period between childhood and adolescence and there is much more of a chance to instill good habits and impart crucial lessons. They're definitely still learning about the world instead of feeling like they know everything