This study investigated the National Board for Professional Teaching Standards' (NBPTS) assessment process in order to identify, quantify, and substantiate learning outcomes from the participants. One hundred and twenty candidates for the Adolescent and Young Adult Science (AYA Science) Certificate were studied over a two-year period using the recurrent institutional cycle research design. This quasi-experimental methodology allowed for the collection of both cross-sectional and longitudinal data insuring a good measure of internal validity regarding observed changes between individual and across group means. Transcripts of structured interviews with each teacher were scored by multiple assessors according to the 13 standards of NBPTS' framework for accomplished science teaching. These scores provided the quantitative evidence of teacher learning in this study. Significant pre-intervention to post-intervention changes to these individual and group means are reported as learning outcomes from the assessment process. Findings suggest that the intervention had significant impact upon candidates' understanding of knowledge associated with science teaching with an overall effect size of 0.47. Standards associated with greatest gains include Scientific Inquiry and Assessment. The results support the claim that the certification process is an effective standards based professional learning opportunity comparable to other human improvement interventions from related domains. Drawing on qualitative data, we also explore three possible implications of teacher learning outcomes from certification upon classroom practice identified as Dynamic, Technical, and Deferred. These patterns suggest that more than one kind of learning may be taking place in relation to board certification. The discussion then considers the importance of this study for policy making and science teaching communities. (Contains 8 tables, 4 figures, and 18 footnotes.)