An undergraduate organic chemistry laboratory experiment that provides an introduction to the concepts and practices of photoredox catalysis is reported. While undergraduate-level photochemistry experiments typically place emphasis on analytical properties of catalysts rather than synthetic applications, this experiment showcases the power and versatility of photoredox chemistry in modern organic syntheses. A hypothesis-driven approach is utilized as students apply chemical reasoning to formulate hypotheses predicting the relative catalytic activity of Ru(bpy)[subscript 3][superscript 2+] and Ru(bpm)[subscript 3][superscript 2+], which differ slightly in ligand structure. Students work collaboratively to obtain conversion data in [2 + 2] cycloadditions catalyzed by Ru(bpy)[subscript 3][superscript 2+] and Ru(bpm)[subscript 3][superscript 2+], and use the data to support or refute their hypotheses. The operationally straightforward experimental protocol has been shown to be robust and reproducible, providing unambiguous results that facilitate student interpretation. Furthermore, the experiment trains students in chemical thinking needed for conducting research.