I was reading the U.S. Government Accountability Office's March 2026 review of K–12 professional development, and what caught my attention was the uncertainty. The meta-analyses it reviewed generally linked professional development with better student test scores. But the evidence was mixed on which specific components were driving those outcomes. Even coaching didn't show the same association across every review. Meanwhile, 67% of teachers in the nationally representative survey cited in the report said collaborative learning with other teachers improved their teaching or their students' learning. That's a report of perceived usefulness, not proof that every PLC works. For me, that is a reminder to stop prescribing a particular format before diagnosing the conditions. What are teachers trying to do differently? What support will they have when they attempt it? And how will we know if the learning is transferring into practice? I'd rather ask those questions first than declare that one PD model is the answer.