The essential role of educational institutions in fostering complex skills, particularly critical thinking, is increasingly recognized. As society undergoes rapid digitalization, individuals must navigate vast amounts of information and misinformation while addressing pressing global challenges. Critical thinking, alongside creativity, remains one of the most valuable and difficult-to-automate skills. It enables individuals to reason effectively, apply evidence-based justifications, and develop solutions across different contexts. Given its significance, equipping teachers with strategies to integrate critical thinking into their lessons is vital. This study examines how secondary school STEM teachers design lessons to foster critical thinking skills within climate change education. Conducted within a professional learning community setting, three Dutch secondary school teachers from STEAM disciplines collaboratively developed a 12-lesson series for an upper secondary Physics VWO-4 class (ages 15–16). Over nine months, they refined their lesson plans, incorporating structured approaches such as the curricular spider web design. Qualitative data analyzed using Boeije’s spiral approach with ATLAS.ti revealed that teachers most frequently employed the critical thinking skill of explanation, particularly justifying procedures, alongside interpretation through decoding significance. Findings suggest key strategies to enhance critical thinking in STEM teacher education, including interdisciplinary collaboration, systematic curricular integration, mentoring, digital tools, diverse pedagogical techniques, and metacognitive skill development. These insights offer valuable recommendations for strengthening critical thinking in STEM education.