BetterLesson empowers K-12 teachers to build a modern classroom: learner-centered, culturally responsive, and personalized. Instead of the conventional (and ineffective) format of professional development for educatorsfilling an auditorium for a day of sleep-inducing lecturesBetterLesson supports teachers for the entire school year with regular, 1:1, virtual coaching. We match each teacher with a world-class coach and then leverage our technology to study actual classroom performance, to suggest customized teaching strategies, to quantitatively measure impact on student learning, and to continuously improve teaching practice through rapid iteration. This process leads to off-the-charts teacher love (our data shows teachers love BetterLesson more than Apple users love their iPhones), high administrator engagement, and, most importantly, dramatic teacher and student growth.