One of Roger's favorite demonstration science lessons is to ask students to determine how long a candle burns in a quart jar. He assigns students to groups of two, making the pairs as heterogeneous as possible. Each pair is given one candle and one quart jar (resource interdependence). He gives the instructional task of timing how long the candle will burn and the cooperative goal of deciding on one answer that both members of the pair can explain. Students are to encourage each other's participation and relate what they are learning to previous lessons (social skills). Each pair lights a candle, places the quart jar over it, and times how long the candle burns. The answers from the pairs are announced. Roger then gives the pairs the task of generating a number of answers to the question, “What factors make a difference in how long the candle burns in the jar?” The answers from the pairs are written on the board. The pairs then repeat the experiment in ways that test whether the suggested factors do in fact make a difference in how long the candle burns.
The next day students individually take a quiz on the factors affecting the time a candle burns in a quart jar (individual accountability) and their scores are totaled to determine a joint score that, if high enough, earns them bonus points (reward interdependence). They spend some time discussing the helpful actions of each member and what they could do to be even more effective in the future (group processing).