This study aims to investigate the applicability and effectiveness of the peer instruction method on teaching the subject of acids and bases at the 12th grade level. In addition, it is aimed to determine the effect of peer instruction on students’ attitudes towards chemistry and in-class discussion, and to examine opinions of students to peer instruction after implementation. The sample of the study consists of 21 12th grade students in a private high school. During the research process, the unit of acids and bases was covered by the researcher with the peer teaching method and implementation was completed in 5 weeks. In this study, which was designed as an action research, qualitative and quantitative data were used together. Quantitative data were collected through acids-bases concept test (ABCT), chemistry attitude scale (CAS), argumentativeness scale (AS), concept questions, and qualitative data were collected through method opinion scale (MOS), semi-structured interview, and observation. The analysis of the data was carried out using quantitative and qualitative methods. The results showed that there was a notable increase in the academic achievement of the students after the implementation. Furthermore, the results obtained from ABCT and semi-structured interviews indicated that peer instruction improved students’ conceptual learning, and also it is effective in eliminating misconceptions. Although the pretest-posttest scores of CAS and AS did not demonstrate a considerable statistical difference, observation and semi-structured interview data pointed out that students’ attitudes towards chemistry and in-class discussion increased positively. At the end of the implementation, it was observed that students’ attitudes towards the peer instruction method are positive and students found it very useful and effective.