This paper uses data from 10 at-scale field experiments in four countries to estimate the effect of inquiry- and problem-based pedagogy (IPP) on students' mathematics and science test scores. IPP creates active problem-solving opportunities in settings that provide meaning to the child. Students learn by collaboratively solving real-life problems, developing explanations, and communicating ideas. Using individual-level data on 17,006 students, the analysis finds that after seven months IPP increased mathematics and science scores by 0.18 and 0.14 standard deviations, respectively, and by 0.39 and 0.23 standard deviations, respectively, after four years. We also identify important gender learning gaps with boys benefiting substantially more than girls. Our approach not only provides strong causal evidence, but also high external validity. These 10 experiments in four countries allow us to examine the effects of IPP across a wide set of geographic, socioeconomic, teacher background, and age/grade contexts (i.e., preschool and third and fourth grades). The results prove to be robust across these different contexts. The 10 RCTs were registered in the American Economic Association Registry for randomized control trials. See the supplementary materials for trial numbers. [Additional funding for this research was provided by the Government of Japan.]