This is an activity where two students work independently to find the equation of a given linear model, then collaborate to check their answers. Partner A has Partner B's worksheet answers, and vice versa. There are specific instructions for each partner to not just "grade" each other's work and give the actual answers, but to help his or her partner find the source of the incorrect answer. This is a great activity to teach students how to monitor their own work with the help of a peer, instead of running to the teacher when they hit a dead end or make a mistake. :)
I have found that this type of activity really helps my students solidify how to write equations from a graph. I like to do this activity the day after I first introduce the topic.