Recent research from the K-12 field indicates that professional development (PD) is a necessary (although not sufficient) factor in improving teacher quality. The research also clearly identifies ways to make professional learning activities for teachers effective. Yet the adult basic education and literacy (ABEL) field is not, for the most part, making use of this evidence in the design and support of PD for its teachers. The dilemma is that evidence-based teacher preparation practice can contribute to improved teacher quality, but it requires restructuring the way PD services are offered to the wide range of ABEL teachers. In this paper, I first review research on PD and professional learning. Then I argue that, intractable as this dilemma between current and evidence-based PD practice seems, it can be addressed through a new conceptualization of the types of knowledge teachers need and the types of PD that will help them acquire and use such knowledge. (Contains 1 table and 1 figure.)