Science is grounded in the processes of inquiry. Therefore, the approach to teaching science should reflect this fundamental characteristic. The problem investigated in this study was to reveal overall differences in science academic achievement, scientific attitudes, attitudes toward science, the nature of science, process skills, and inquiry ability, produced by the teaching of science as inquiry as compared to traditional methodology. The purpose of this study was to investigate quantitatively the above questions, concerning the teaching of science as inquiry as compared to traditional methodology across available experimental studies that have been reported.The researcher used a systematic search of the literature from electronic database, the ancestry approach and related Journals to locate thirty-four reading comprehension instruction studies. The effect sizes were calculated by Hedges and Olkin’s (1985) procedure. Further, this study tested all coded features by ‘Categorical Model ‘to find moderator variables.The analyses revealed that teaching science as inquiry increased students' science academic achievement, attitudes toward science, the nature of science, process skills, and inquiry ability all at a significantly higher level than was the case for students taught science by traditional approach. On the other hand, scientific attitudes were not improved at the hypothesized level for significance. However, most effect sizes were low and moderate. Science academic achievement: d+=0.5353, scientific attitudes: d+=0.1992, attitudes toward science: d+=0.5082, the nature of science: d+=0.3529, process skills: d+=0.3477, inquiry ability: d+=0.3692. Based on the results of the study, the researcher also provided a discussion and made some recommendations.