Critical thinking (CT) which is self-regulatory thinking process includes some skills like interpretation, analysis, evaluation, inference and evidence questioning. There are skill-based, content-based and mix CT teaching approaches in literature. It is important to find out how effective these approaches are on CT skills rather than whether they are effective on CT. So this study aimed to determine to what extent the content-based and skill-based teaching of CT is effective in improving the CT skills. 21 results of 17 research studies were included in the meta-analysis. The content-based teaching of CT is strongly effective in improving students' CT skills. This effect level does not differ significantly by whether the sample group is gifted or normal students and by educational level of sample groups. Also, the skill-based teaching of CT is strongly effective in improving students' CT skills. Besides, the effect size of the studies which applied the skill-based teaching of CT is higher than the effect size of the studies which applied the content-based teaching of CT. However, there is no significant difference between these two approaches in terms of improving CT skills. So skill based and content based critical thinking teaching approaches can be used for all students from different education levels to improve critical thinking skills.