Investigated the effects of 3 kinds of instructional support on students' inquiry learning. In a computer-based simulation setting for inquiry learning of scientific principles, 79 students (53 female, 15-16 years old) from 2 Swedish schools were divided into a basic-inquiry group (22 participants, received only basic inquiry support), an explanation group (29 participants, received only explanation prompts), and a regulation group (28 participants, received both explanation and regulation prompts). A knowledge test and an application (transfer) test were completed after an introductory lesson, a knowledge pretest, and the varying experimental learning conditions. Results show that regulation prompts have a positive effect on students' test performance in both the knowledge and application test, with the regulation group outperforming both of the other groups. Interestingly, the explanation group did not outperform the basic-inquiry group. Also, the regulation group seemed to have internalized the regulation of their flow of thoughts since even in the absence of regulation prompts these students outperformed the other groups in terms of scientific reasoning. Possible reasons for the lack of a significant effect of explanation prompts on learning outcomes are discussed.