Commentary: The Need for Theories of Change in Training and Technical Assistance: Where the Rubber Meets the Road.

In this commentary, I revisit some of the core issues raised in both the first and second special issues on "Strengthening the Science and Practice of Implementation Support: Evaluating the Effectiveness of Training and Technical Assistance Centers." I first outline the concerns that I think are of paramount importance and then very briefly dissect each one from the perspective of a prevention scientist. I add commentary where I think the field can benefit and strengthen to advance the "science" of implementation support. At the same time, I also raise several points that I think will contribute to a better understanding of "how" TTA works, for "whom" and under what conditions. This portion of the commentary attends to the different training and learning modalities used for TTA, the argument that capacity building should be the objective, decluttering the constructs of motivation and readiness, and whether we can ever validly assess a public health impact from TTA. I offer suggestions to address each concern and hope that the field can benefit from this discussion as we usher in a new era.