The purpose of the present study is to examine the effectiveness of a metacognitive prompts intervention-science (MPI-S), which is based on the nature of science with 162 eighth-grade science students. It was hypothesised that students exposed to the intervention will show higher levels of content knowledge and knowledge about the nature of science than students in a comparison group. Attempts were also made to determine what cognitive processes are triggered during the use of metacognitive prompts. Findings showed significant improvements in students' content knowledge and nature of science. In addition, qualitative findings revealed that the experimental group made choices based on evidence in the inquiry unit whereas the comparison group made decisions based on authority. Educational implications for practice into the classroom are discussed. (Contains 2 figures and 3 tables.)