The National Board for Professional Teaching Standards (NBPTS) was established in 1987 and charged with the mission of improving the quality of teaching and public education. The National Board certification system involves three critical elements: (1) standards setting; (2) assessment instruments; and (3) professional development. This Digest discusses the National Board's research and development activities designed to develop an assessment system that meets the NBPTS criteria. The standards setting process and assessment development and implementation processes comprise the two main components of the National Board's research and development agenda. The National Board believes that a unitary certificate suggesting proficiency in teaching all subjects to all students of all ages is unwarranted. Consequently, NBPTS is establishing standards committees in each of 30 certification fields to define standards and student age levels. The NBPTS assessment system will be performance based and will employ a broad range of strategies. The first assessment will be launched in early 1993, and the full system of National Board Certification will be completed by the 1998-1999 school year. Five references are included. (LL)