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 aims to determine the effect of peer instruction on students' attitudes towards chemistry and in-class discussion, and to examine students' opinions regarding peer instruction post-implementation. The sample of the study consisted of 21 students studying in their 12th grade at a private high school. During the research process, the unit of acids and bases was covered by the researcher using the peer instruction method and the implementation was completed over a 5-week period. The study was designed as an action research, with both qualitative and quantitative data collected and examined. The study's quantitative data were collected through the Acids-Bases Concept Test (ABCT), Chemistry Attitude Scale (CAS), Argumentativeness Scale (AS), and concept questions, while the qualitative data were collected through the Method Opinion Scale (MOS), semistructured 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 the students' conceptual learning, and was also effective in eliminating their misconceptions. Although the pretest-posttest scores of the CAS and AS did not demonstrate a considerable statistical difference, the observation and semi-structured interview data highlighted that the students' attitudes towards chemistry and in-class discussion increased positively. At the end of the implementation, it was observed that the students' attitudes towards the peer instruction method were positive and that the students considered it to be very useful and effective.