This study was a mixed quantitative-qualitative research to evaluate the efficacy of a designed student-centred instructional (DSCI) program for teaching about acids and bases. The teaching innovation was designed based on constructivist, hands-on inquiry and context-based approaches and implemented in seven 45-min lessons with a class of 36 grade 11 students (experimental group) from a public senior high school in Indonesia. Another class of 38 students (comparison group) from the same school was instructed using a traditional teacher-centred approach. Data were obtained using a (1) 12-item achievement test on acids and bases that was administered to both groups as a pretest and a posttest, (2) self-evaluation 13-item questionnaire on students' perceptions of their competence and confidence in carrying out the inquiry activities that was administered to the experimental group and (3) 3-item open-ended questionnaire on students' perceptions of the instructional process using the DSCI that was administered to the experimental group. The results of the study showed that the teaching innovation was effective in improving students' understanding of acid-base concepts with significant difference between the two groups on the posttest mean scores. Moreover, the effectiveness of the innovation was supported by an increase in students' interest in learning science as indicated by their (1) positive perceptions of their engagement and competence in doing inquiry activities, (2) positive perceptions of the learning environment and (3) positive outcome expectations. The findings have implications for chemistry teaching in any institution with similar achieving students as well as for the professional development of teachers.