Learning and development of critical thinking (CT) skills in higher education is essential for academic achievement. The following experiment is the first to examine the effect of online student's perceptions and attitudes towards CT across dimensions of confidence, valuing, misconceptions, cognitive reflection, and authors writing. Furthermore, a CT intervention was developed, and the effects of the intervention examined with an aim to help students improve their grade point average. The analyses demonstrated that student's confidence and cognitive reflection predict academic achievement. Moreover, the online CT intervention was associated with improved students' CT attitudes, skills, and academic performance. Significant interactions were observed between time (pre- and post-intervention) and intervention in cognitive reflection, confidence, beliefs, and attitudes related to CT, and student grade point average (GPA, as a measure of student's performance on online modules). It was concluded that the CT can be taught and that an intervention based on "how to think" rather than a "what to think" mixed approach can help online students develop CT, strengthen their confidence in CT and help students improve their academic performance in an online setting.