This quasi-experimental study investigates the effects of an instructional intervention based on Marzano’s New Taxonomy on critical thinking development in seventh-grade students. Using the Solomon Four-Group Design, 180 students were randomly selected from a government girls' high school in Haripur, Pakistan. The intervention emphasized Marzano’s self-system and metacognitive system to foster cognitive engagement and analytical reasoning. Over three months, students participated in structured activities aimed at enhancing critical thinking. The Figural Intersection Test, assessing working memory where critical thinking occurs, was used to measure impact. Results indicated significant improvement in students’ critical thinking skills, with history and maturation having no notable influence—reinforcing internal validity. These findings suggest that the intervention, rather than external factors, led to the observed gains and underscores the broader applicability of Marzano’s framework in enhancing critical thinking within educational contexts.