Inclusion of a diverse group of students, both regular learners and learners with special needs in chemistry classrooms is an important goal of chemistry educators. However, alternative conceptions in chemistry among high-school students can be a barrier for completing the learning process in the classroom, especially in a heterogeneous class. This study aimed to examine differentiated instruction (DI) in a chemistry classroom. We evaluated how customized pedagogical kits (CPKs) for DI, which aim to overcome alternative conceptions found during chemistry instruction, affected students and teachers. This paper presents the findings of a mixed-method study that was conducted with 9 high-school chemistry teachers, and 551 chemistry students. We used a pre-post questionnaire to investigate the impact of CPKs on teachers' and students' self-efficacy beliefs and attitudes towards chemistry and differentiated instruction, in addition to students' achievements. The findings indicated the significantly higher averages of self-efficacy beliefs and attitudes towards DI in chemistry among teachers and high-school students, in addition to the significantly higher performance of students in chemistry tasks after implementing CPKs in classrooms. Being aware of the limitations of DI, we discussed customized pedagogical kits as a means that can support better inclusion in chemistry education.