The authors present the National Science Foundation project, Teachers Investigating Adult Numeracy (TIAN), a collaborative project of the Center for Literacy Studies at the University of Tennessee and the Technical Education Research Centers, Inc. (TERC) in Cambridge, Massachusetts. The project has developed and tested a model for inservice professional learning that engages adult education teachers in considering how to implement purposeful and effective mathematics instructional approaches. In this article the authors explain the project's perspective on sound mathematics learning and teaching, describe the professional development model created to support teachers' growth in that arena, and finally present some data about teacher-participants indicating positive shifts in instructional practice. (Contains 5 tables.)