This study compares learning from designing instruction in the context of simulation-based inquiry learning with learning from expository teaching. The domain of instruction was the electricity domain of high-pass and low-pass filters. Participants were students from a technical vocational school. In the experimental condition ("N" = 21) students created assignments for an imaginary student to help this student to learn from a computer simulation. The LOOK-EXPERIMENT-DESIGN (LED) approach was developed to support students in designing these assignments. This support structure scaffolded students in orienting themselves in the simulation (LOOK), in performing experiments to gain more insight into the simulated domain (EXPERIMENT), and in designing assignments (DESIGN) about the simulated domain. Students in the control condition ("N" = 28) received traditional instruction. Students came from two different classes and were divided over the two conditions. After 3 two-hour lessons, all students completed a test measuring conceptual and procedural knowledge. Results showed that, in one class, students who learned by designing assignments performed significantly better on test items measuring conceptual knowledge than students who learned from traditional instruction. This was not replicated in the other class. No differences between the conditions were found for procedural knowledge. (Contains 5 tables and 4 figures.)