Improving student achievement through professional development (PD) is both highly sought-after and elusive. This four-arm randomised controlled trial evaluated effects of Quality Teaching Rounds (QTR), a pedagogy-focused form of PD, on mathematics, reading, and science outcomes for elementary students (n = 5478). Outcomes at baseline and 8-month follow-up were compared for QTR, QTR trainer-led, peer observation, and wait-list control groups. Students in the QTR group made 25% more progress in mathematics than the control group (g = 0.12, 95% CI: 0.07e0.17). This result supports QTR as a form of PD with significant potential for wider impact. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Improving student achievement through professional development (PD) is both highly sought-after and elusive. This four-arm randomised controlled trial evaluated effects of Quality Teaching Rounds (QTR), a pedagogy-focused form of PD, on mathematics, reading, and science outcomes for elementary students (n = 5478). Outcomes at baseline and 8-month follow-up were compared for QTR, QTR trainer-led, peerobservation, and wait-list control groups. Students in the QTR group made 25% more progress in mathematics than the control group (g = 0.12, 95% CI: 0.07e0.17). This result supports QTR as a form of PD with significant potential for wider impact. ? 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND