The introductory freshmen electromagnetism course at MIT has been taught since 2000 using a studio physics format entitled TEAL--Technology Enabled Active Learning. TEAL has created a collaborative, hands-on environment where students carry out desktop experiments, submit web-based assignments, and have access to a host of visualizations and simulations. These learning tools help them visualize unseen electromagnetic concepts and develop stronger intuition about related phenomena. A previous study has shown that students who took the course in the TEAL format (the experimental group) gained significantly better conceptual understanding than those who took it in the traditional lecture-recitation format (the control group). The present longitudinal study focuses on the extent to which these two research groups (experimental and control) retain conceptual understanding about a year to 18 months after finishing the course. It also examines students attitudes about whether the teaching format (TEAL or traditional) contributes to their learning in advanced courses. Our research has indicated that the long-term effect of the TEAL course on students' retention of concepts was significantly stronger than that of the traditional course. This research is significant because it documents the long-term cognitive and affective impact of the TEAL studio physics format on learning outcomes of MIT students.