The french horn is an extremely diffucult endeavor for the high school band student for the simple fact that you cannot march in marching band with your instument. You are forced to switch instruments, usually to pit percussion or mellophone.
The reason for this is quite simple. Horns are expensive, a decent one costing approximately six thousand to ten thousand US dollars.
So what's so difficult about the switch? The mellophone is played like a trumpet, which is right handed. So your marching french hornist has to learn new fingerings and develop new muscles in both hands.