I like to load up my students with lots of material to work on. This isn't meant to overwhelm them or take up every speck of free time they have. Rather, it gives them options over the course of the week and prevents dead time during their lessons.
If I give them only enough material to take up exactly one half-hour or hour lesson, chances are high that they will get bored or burn out during the week. I'd rather give them the choice of where to focus their energy; facilitating the choice to turn their attention to one area or another of their musicianship is part of my job as their teacher.
We start small; I might give them a few more scales to practice than would be practical to hit all in one day. When that becomes comfortable, I move on to assigning more than one etude at a time, usually tailored toward whatever pieces the student is currently working on. When we get to this point, I make it a point to talk to my students about seeing their practice progress in terms of the week, not just in terms of what they accomplish in one day. This leads naturally into a discussion about how to plan out their practice time, as well as how to isolate areas in their pieces and etudes and practice those areas in a deep, meaningful, and inquisitive way.
Having lots of material to choose from also helps me give the best lesson experience I can; if a student only has one piece or etude to bring into a lesson, and they walk in and tell me they didn't practice it, that limits how much real progress we can make that week. But I've found that if my students have a slightly wider array of options, they usually find something that interests them enough to inspire focused practicing.
My ultimate goal is to prepare my students for college-level music programs, in which they would be expected to balance the expectations of their private teachers with those of their orchestra and band directors. Between recital prep, competitions, auditions, and large ensemble rehearsals, the stack of music on the to-do list can get pretty tall. I want my conservatory-bound students to be able to prioritize all these demands without feeling like they're drowning.
And in the end, it's gratifying for me to see a student take ownership of their own learning process; after all, my job is to make sure they eventually become their own teachers.