This research reports data from case studies of three intermediary organizations facing the challenge of scaling up teacher learning. The turn of the century launched scaling-up efforts of all three intermediaries, growing from intimate groups, where founding teachers and staff were key supports for teacher learning, to large multistate organizations. The authors draw on data from three earlier qualitative studies, as well as newly gathered data on professional development at Big Picture Learning, Expeditionary Learning, and the Internationals Network, and reveal some of the challenges and benefits of taking teacher learning to scale.