This work, based on a model professional development programme, gives powerful proof that urban teachers can ignite curiosity and promote deep understanding in children when provided with the necessary intellectual infrastructure - including a complex balance of increased science knowledge, a safe environment for professional experimentation, and a long-term interaction with colleagues. The ensuing invigoration and renewed dedication of programme participants belies the inevitability of the projected national science teacher shortage. Elnora S. Harcombe explores professional teacher development based on a constructivist learning theory. She asserts that, framed in the knowledge domain of the sciences, this learning theory empowers teachers to change what they know, how they teach, and what their students learn.