This report examines the potential of adaptive testing, two?-stage testing in particular, for improving the data quality of the National Assessment of Educational Progress (NAEP). Following a discussion of the rationale for adaptive testing in assessment and a review of previous studies of two-?stage testing, this report describes a 1993 Ohio field trial of two-?stage assessment carried out, under the direction of the authors, by the National Opinion Research Center (NORC). The trial was part of a larger methodological study of science assessment at school-?leaving age supported by the National Science Foundation (NSF) and the Office of Educational Research and Improvement (OERI). This report summarizes the instrument design, procedures, and results of the field trial and discusses implications for the conduct of assessment generally, and for NAEP specifically. A technical appendix outlines the measurement justification for two design prototypes and describes procedures used in analyzing the data. [This paper was commissioned by the NAEP Validity Studies (NVS) Panel May 1998.]