This study addressed changes in teachers' perceptions of their teaching skills after completing the portfolio requirements in the first field test for the National Board for Professional Teaching Standards Certification and their reactions to the certification requirements. Background information on the National Board, descriptions of the portfolio requirements in the areas of Early Adolescence/Generalist and Early Adolescence/English Language Arts, and results of quantitative and qualitative data are presented. Forty-eight teachers from seven field test sites participated in the study. The results of both the quantitative and qualitative data indicated that teachers perceived portfolio assessment as improving their teaching. They further described portfolios to be challenging, time consuming, and supportive of reflective processes. (Contains 17 references.) (Author/ND)