Background:
The purpose of this study is to determine the effect of an activity set developed according to the inquiry-based learning approach in the unit “Particulate Structure of Matter” on students’ critical thinking skills in science and technology courses. The study was conducted with 90 sixth grade students attending four sixth grade classes of a secondary school.

Material and methods:
Within the framework of the study, in order to evaluate the effects of inquiry-based learning approach on the students’ critical thinking skills in science and technology courses, the guided activity set was developed by the researchers in line with the inquiry-based learning approach. In this study, pre-test and posttest control group experimental designs were used.

Results:
The findings of the study revealed that science and technology learning supported with the guided activities developed in line with the inquiry-based learning approach have significant effects on students’ critical thinking skills in science and technology courses.

Conclusions:
The critical thinking level of the experimental group students taught with the inquiry-based learning approach was found to be higher than that of the control group students taught with the traditional lecturing method.the critical thinking level of the experimental group students showed a positive increase in all the dimensions.