Terracotta is an experiment-builder integrated with a learning management system (LMS), allowing a teacher or researcher to randomly assign different versions of online learning activities to students, collect informed consent, and export deidentified study data. Terracotta is a portmanteau of Tool for Educational Research with RAndomized COnTrolled TriAls, and is designed to lower the technical and methodological barriers to conducting more rigorous and responsible experiments in education.