The research aim was to identify the effect of revising the thematic unit "Changes in Chemical Reactions" using IBSE (based on confirmation inquiry) in the 8th grade of secondary school. This thematic unit is taught in chemistry lessons in the 2nd term of the 7th grade. A set of activities verified by a piece of pilot research was used to implement IBSE based on confirmation inquiry using the 5E Educational Model. The research was performed in ten Slovak secondary schools during the 1st term of the 2017/2018 school year. This research employed the quasi-experimental methodology involving pre-test--post-test two-group design. The research sample consisted of 292 8th grade students. They were divided randomly into a control (n=149) and experimental (n=143) group, and the intervention took place during 10 lessons. Cognitive tests based on the revised Bloom's taxonomy were used to measure students' knowledge and skills before and after revision. The results indicate that using IBSE (based on confirmation inquiry) in the revision phase is more effective than teaching without using IBSE in terms of developing conceptual understanding. It affects the lower and higher cognitive processes (understanding, application, and analysis) and stimulates learning mainly in students with lower academic performance.