If they don't take the initiative and practise frequently (without you having to coax them) then you and the school are being patronized and they're just going thru the motions.

If one truly loves playing an instrument and making music, they should NEVER have to be TOLD to practise, because in that mindset it's not "work" or a "chore" and it's more a case of prying them away from the instrument in order to deal with other chores/responsibilites.

My $0.02