This study investigates the effects of an intensive 1-week Inquiry-Based Science and Technology Enrichment Program (InSTEP) designed for middle school-aged female students. InSTEP uses a guided/open inquiry approach that is deepened and redefined as eight sciences and engineering practices in the Next Generation Science Standards, which aimed at increasing female students' interest in science and science-related careers. This study examined the effectiveness of InSTEP on 123 female students' pre-assessment and post-assessment changes in attitudes toward science and content knowledge of selected science concepts. An attitude survey, a science content test with multiple-choice questions, written assignments, and interviews to collect data were all used to measure students' attitudes and content knowledge. A within-group, repeated measure design was conducted, and the results indicated that at the post-intervention level, InSTEP increased the participants' positive attitudes toward science, science-related careers, and content knowledge of selected science concepts.