Boston teachers boost their skills and student proficiency through peer observation and collaboration. The observation is the anchor activity for a learning site, a professional learning series designed to support teachers in making instructional improvements aligned with self-identified needs and districtwide instructional goals. Learning sites are one of the core professional learning offerings by a team of teacher leaders in Boston Public Schools called the Telescope Network. The network's aim is to weave together the collective expertise of classroom teachers and district instructional coaches that exemplify meaningful, connected professional learning for educators. In the article's example of a 10th-grade biology class site and similar sites across the district over the past few years, hundreds of Boston educators have observed an effective peer and have integrated new teaching strategies into their practice.