This study examined how types of tasks influenced student activities/thinking and defined the role of Seatwork in mathematics lessons. It used 60 lessons from the TIMSS videotaped Study. These data indicated that practice was the most prevalent form of tasks in the U.S. In Germany, students completed mathematical calculations after a complex problem-solving segment. In Japan, teachers combined practice of routine procedures in Seatwork with opportunities to prepare material, think about problems, and explore concepts. Findings expand our understanding of how tasks organize learning opportunities and effect how students come to understand mathematics. (Contains 12 figures.)