Ask your student to explain and demonstrate what is on the assignment sheet. Not to supervise or confirm that he is or is not doing it correctly, but just to become familiar with what is going on at our lessons. This conversation is good for both of you, and helps you avoid the risk of being perceived as a second teacher.
If he can’t explain a practice procedure, or if you believe that he has misunderstood the practice instructions, give me a call or send an e-mail so we can discuss it at the next lessson. I try to focus on specific issues each week, rather than try to change everything all at once: he may find this discouraging.