I have a 20-sided die (check math department or gaming store) placed inside a clear container. This container keeps the die on the tables and makes it easier to pass. Before a test, I prepare 20 questions that relate to the topic we are studying, and I number each question. Students take turns rolling the die. The number they roll is the question they must answer. A correct answer earns a point for the student's team. The winning team gets bonus points on the test. The best part is that all the students must listen carefully because they could roll the same number as another student, and boy, do the teammates get upset if a student answers incorrectly after the answer was just announced by another student! If there is time after one round, I allow teams to study quickly with their teammates for five minutes before round two. They can look up questions that they couldn't answer the first time. Finally, if you tell them the teams when you begin the unit, the stronger students will help the weaker ones to learn throughout the unit in hopes of winning the game at the end of the unit.