Imagine teachers, administrators, and university mathematicians and staff learning together in a lab setting where students are excited about attending a week-long summer math event because they are at the forefront of the experience. Piloted in three New Mexico classrooms during summer 2014, MathLab expanded into 17 lab settings over six locations during summer 2015 and was implemented again in 2016. The enthusiasm of all participants witnessed by the New Mexico Public Education Department has resulted in funding to support future events. MathLab is an innovative learning design from New Mexico State University's Mathematically Connected Communities (MC[superscript 2]), a partnership of New Mexico educators that includes mathematicians, school leaders, researchers, and teachers. Aligned to Learning Forward's Standards for Professional Learning, MathLab began as an idea to shift from traditional one-shot professional development to ongoing professional learning situated in K-12 mathematics classrooms. This article discusses: MathLab's goals; what MathLab looks like for teachers and administrators; MathLab's framework; MathLab's results and impact; and what happens after MathLab.