Simulations, which is a type of educational technology has started to be used widely in classes. Contradictive results show that there is no certain conclusion about the effects of them on students' domain knowledge, inquiry skills and attitudes towards science. The goal of the study is to compare the impacts of simulation-based and textbook-based instructions on the middle school students' science achievement, inquiry skills and attitudes towards science. The study was done with 188 middle school students and three science teachers. Whereas 98 of them enrolled in the classes where simulation-based instruction was used, 90 of the participants were from the classes in which textbook-based instruction followed. A quasi-experimental research design was used in the study. The data was gathered by the achievement test, the inquiry skills, and the attitude scale. The findings revealed that simulation-based instruction is significantly efficient in enhancing middle school students' science achievement and inquiry skills. Yet, it was also reached that both of the instructions have no significant impact on students' attitudes towards science. Possible reasons behind the results were also discussed.