In March of 1999, the Professional Development Laboratory (PDL) of the New York University School of Education conducted an Evaluation Forum to address the issue of evaluating professional development. The Forum engaged PDL stakeholders, educational leaders, and community supporters in generating and responding to critical questions related to assessing professional development's impact on student learning. In addition to over 80 attendees, 8 national leaders in professional development served on a panel to offer recommendations, facilitate small group discussions, and respond to questions. The Forum addressed the following: (1) the context for professional development (public accountability and standardized tests, and teacher shortage); (2) what is known about professional development (resource drive decisions, complexity of teaching and professional development, culture of collaboration, and the difference the principal makes); and (3) evaluation of a PDL program (the PDL's theory-in-use, necessary agreements, whether the evidence is a result of PDL alone, effective strategies for collecting evidence, and where a PDL could collect evidence). Three appendixes contain a PDL overview, the Evaluation Forum panelists and guests, and the Evaluation Forum agenda. (SM)