In complex educational systems, stakeholders with varied interests often put the greatest value on singular, summative outcomes tied to high-stakes tests. While those summative outcomes are useful and important, an investment in teacher learning intended to improve student achievement is also a treasure worth pursuing. So how do we, at a systems level, know that our investment in teacher learning is making a difference? How do we ensure that professional learning is impacting teacher practice in a way that leads to improved student outcomes? As professional development providers for myPD (an online, personalized professional growth system) in Long Beach Unified, a large urban school district in California, we feel a responsibility to wrestle with these questions. We want to deliver high-quality professional learning that ultimately