Addresses AP® Chemistry Big Idea 4 and Learning Objective 4.1. Investigate factors that affect reaction rate using the iodine clock reaction. Change temperature, concentration, and surface area of solid reactants and add a catalyst to observe changes in reaction rates. The iodine clock reaction provides an easy visual cue to measure reaction times. Reaction rates are explained using physical phenomena, such as molecular collisions. Materials are sufficient for 30 students in teams of 3.