This very broad question was put to several prominent teachers.
The first response:
COMPETITION motivates most students, including honor bands or solo and ensemble work. Sometimes, the fear of public performance is enough!
CHAMBER MUSIC is much more fun practicing etudes. There are plenty of duos or quartets that a teacher can assign in order to l instruct and be fun.
To motivate pre-teen/teens: you simply have to find music they LIKE. For American boys, this may well be cowboy-inspired tunes, music they know from the movies, the latest pop tunes, or evergreen classics.
If you want to get students to practice range, get them to WRITE THEIR OWN exercises. They will practice these more than the ones you assign - for around six weeks with young teens.
The following user(s) said Thank You: Tobias Heinz