Catherine Lewis, Ph.D. is a research scientist at Mills College at Northeastern University (Oakland, California campus) who has directed 10 major federal grants focused on instructional improvement. Her randomized trial of teacher-led lesson study with Japanese mathematical resources (Lewis & Perry, JRME, 2017, 48:3) was identified by a What Works Clearinghouse-criteria review as one of only two studies of mathematics professional learning (of 643 reviewed) to improve students’ mathematical proficiency. A developmental psychologist fluent in Japanese, she has makes Japanese elementary education practices and materials available to U.S. educators, including lesson study (teacher-led, classroom-based professional learning), and Mathematics Teaching Through Problem-solving (an approach in which students build each new mathematical idea in the curriculum). School-wide lesson study enables a shift to powerful mathematics learning and dramatically improves mathematics achievement in urban schools.