This paper describes a series of projects on the design and implementation of "conceptual labs" aimed at developing insightful learning, following work that began in 1994/1995. The main focus has been on courses in mechanics and electric circuit theory. The approach taken in designing these innovative curricula can be described as "design-based research". A common feature in these learning environments is the use of technology as a tool to aid students' inquiry. In addition, systematic variation, based on the theory of variation, has been introduced into the design of the assigned tasks. Results from conceptual inventories have demonstrated the success of conceptual labs. In the later projects, video recording was used to study students' courses of action in labs. This paper describes how these studies have provided insights into conditions that are critical for learning and how these insights have helped the present author and his co-workers make further improvements to learning environments. (Contains 1 table and 8 figures.)