"Practice makes perfect, but only if you do it right." Typical physics students practice extensively through the large quantities of homework they do. But research in introductory physics instruction shows that despite this practice, students often do not learn much in introductory physics. Students often do not focus their practice on the skills (such as concept interpretation, and generating a physical representation of a problem) that they need in order to solve physics problems flexibly and reliably. They often focus their practice instead on simply getting an answer. By omitting practice of important skills, it is likely that those skills will not be learned. This paper identifies communication difficulties between students and between students and instructors as important sources of barriers to achieving high-quality student practice. Some strategies to address communication difficulties in the context of small group in-class problem solving are proposed. A classroom peer-collaborative structure, Supervised Practice, that implements these strategies is described, and the impact of the classroom design on the quality of student practice is investigated.