One of the most challenging things for music students and their parents is finding a successful set of practice habits. That can include time, place, frequency, access, strategy and more. These questions come up so often with parents - and there aren't really right or wrong answers.
Like everything else having to do with humans, it's different for each of us!!!
Break it up
One suggestion I like to share with my middle and high school aged students, for whom practice is 45-60 minutes per day, is to break it up.
Some students have really enjoyed doing 15 minutes of practice (scales), then one subject's homework; then 15-20 minutes of practice (etude), another subject's homework; then 20 minutes of practice on repertoire.
This method refreshes the brain, breaks up the monotony, and improves focus on each segment of both the practice and the homework. Simply moving from place to place instead of staying seated working on the same thing for a long stretch is useful.
This is an effective way to practice - check out this TED talk on practice for more perspective on this approach.
What works best for your student?