The Teamwork Indicator (TWI) inventory for students monitors group development and can serve as a feedback tool in project work, active learning, and teams to improve the educational outcome. TWI consists of 20 items, it is simple and easy to use, and the inventory gauges changes over time in four central group dimensions: management, social collaboration, work commitment and attitudes toward evaluations. Based on a large sample (N=6595), the inventory has good psychometric properties. The item structure showed temporal and contextual stability for sex, cultural diversity, language, and training format. In active learning, students are left more to themselves, and in peer assessment, the inventory can partly substitute for feedback from a facilitator. The TWI is suitable for groups of a certain duration and with two-fold goals: content learning and social development of interactive, communication and collaborative skills. The use of TWI can initiate reflections about self, team and group functioning in general, which in the short and long-term is likely to translate into the outcome of new groups, probably also into the students' future careers.