The article deals with the problem of the impact of attestation on teachers' professional development, particularly the question of what the theoretically grounded content of the methodology aimed at assessing the effects can be. The study is based on the premise that the quality of attestation procedures, determined by their validity and reliability, directly affects the professional development of teachers. Comparative analysis of approaches to validation of evaluation processes, review of attestation materials, and modeling of the methodology based on S. Toulmin's reasoning system were used to define the theoretical framework and address the research question. The theoretically grounded content of the method is based on the approach of M. Kane and the principles of construct validity, where validity is determined through the analysis of sequential interpretive arguments (statements) adapted to the attestation. This allows us not only to evaluate the logicality and consistency of the proposed arguments but also to check their validity and compliance with the stated objectives of the attestation. Consequently, the methodology provides an opportunity for the realization of more fair and effective attestation procedures that contribute to the professional development of teachers. The article also offers recommendations for the methodology to increase the potential of its application.