Every three years the Program for International Student Assessment (PISA) issues a test to evaluate education systems worldwide by assessing the skills and knowledge of 15-year-olds. While any test has limitations and critics, PISA warrants our attention as it is one of the few means of comparing U.S. student achievement to global peers. Results of the most recent test, administered to almost half a million students and representing 28 million students in 72 participating countries, were released in December. PISA 2015 focused on science, with reading, mathematics and collaborative problem solving as minor areas of assessment. Singapore outperformed all other participating countries in science. Japan, Estonia, Finland and Canada, in descending order of mean science performance, are the four highest-performing OECD countries. The U.S. ranks in the middle, about the same as the last time the assessment was administered in 2012. An analysis of the findings indicate that what matters in science outcomes is how much time students spend learning science and how science is taught. In almost all education systems, students score higher in science when they reported that their science teachers frequently explain or demonstrate scientific ideas, discuss students’ questions and adapt lessons to students’ needs and knowledge, or provide individual help when students have difficulties understanding a topic or task. While these findings may not surprise independent school educators they may serve to reinforce the importance of these instructional practices in advancing student learning.