The main purpose of this research was to examine how the Argument-Based Inquiry (ABI) approach affects students’ science achievement, inquiry skills, and scientific writing skills and to determine what the students thought about the ABI. This study employed an explanatory sequential mixed methods design using a quasi-experimental research method in which a pretest-posttest control group was used in the quantitative part and semi-structured interviews were conducted in the qualitative part of the research. The participants included 47 fourth-grade students attending a public elementary school. The students in the experimental group were taught four science units using the ABI approach, while those in the comparison group were taught the same units with the teacher’s own teaching methods. Independent samples t-tests were conducted for the analyses of data collected through Science Achievement Tests, the Inquiry Skills Test, and the Grading Rubric for Scientific Writing Skills. The findings revealed significant differences between the experimental and comparison groups in terms of science achievement, inquiry and scientific writing skills in favor of the experimental group. Content analysis of the qualitative data revealed that the students held favorable opinions about the ABI approach. We concluded that the positive effects of the ABI approach continued to increase throughout the study.