I hear many teachers lament that if a student doesn't practice (adequately), they will make no progress, and the same lesson will be repeated over and over, and lessons will be no fun for the student or the teacher.
I have to wonder, then, what is being taught at the lesson? If a student has weekly lessons, they should learn new things every week, regardless of how much they practice. And if they learn new things every week, by definition they are making progress, and are not getting the same lesson repeated each week. And, the learning and teaching of new things should be fun, challenging, and rewarding for both student and teacher, always!
In my education and career I have experienced many teachers, observed many teachers, and coached a few teachers. I have noticed that a large number of teachers follow (basically) a "perform, critique, assign" process in the lesson. Student performs. Teacher critiques the performance and works with student on a few things related to the performance. This could repeat for multiple pieces or exercises. If student's progress is satisfactory, teacher assigns new material. Otherwise, no new material. (So, progress or no progress is essentially a consequence of satisfactory performance.) If there is something within the material a student is unfamiliar with, teacher will explain/teach. (So, teaching is often coincidental, fleeting, possibly of secondary importance, or may not occur at all.)
Consider an alternative process that might be called, "teach, practice," that can work very well for all students, but especially for students who don't practice enough at home and for students with anxiety or other challenges and struggles where the conventional strategies don't work as well or result in disappointment and frustration (and too often animosity toward students and parents).
Lessons begin with learning something new. A planned lesson. This can include review of prior knowledge, reinforcement, scaffolding of concepts and skills, etc. But always something new. Then, practice. Drills, repetition, playing small exercises, off-instrument work, ear training, listening and analysis, practicing small sections of repertoire. The practice can be all about getting better at things already known, or also about learning new things, but it's real practice, not performance. Then, the assignments flow from this practice in the lesson: essentially, to do more of what we've been doing together, on your own. But, whether they do or not, the student has learned new things and gotten better at some things in the lesson. They never, ever, walk away empty handed. The parent never, ever, wastes their money.
Performance grows out of the practice in the lessons when students are ready. They may be eager to perform at some point. Teacher may want to challenge them at some point. The performance for the teacher should result in positive feedback, and then the teacher will know what to practice with the student (this is formative assessment). No need for critique, per se. No need for disappointment and frustration and animosity.
Teacher teaches and gives much guided practice with student. That's the lesson. Student may or may not practice independently at home. But they will make progress. And the chance that they will grow to love music and practice more on their own down the road remains. And we're really teaching, not simply assigning students to go learn on their own, and get consequences of "no new assignment/no learning" if they don't do what they were previously assigned well enough, or don't perform adequately for the teacher.
Try this and I can virtually guarantee every student will make progress. Even more progress if you're teaching them things they really want to learn and in ways they can relate to and find relevant. And let's never say negative things to colleagues about students, even if they don't practice. It's our job to reach them, to teach them, to help them grow... every lesson!