Past research on the effects of Minimum Competency Tests (MCT) on teaching and learning is reviewed, and the large database of the National Assessment of Educational Progress (NAEP) is used to shed more light on these effects. There seems to be little doubt that MCT, together with associated changes in instructional methods, has produced some substantial changes in student performance. The influence of state-mandated MCT on the quality of teaching and learning as reflected in the NAEP was investigated by comparing the performance of participants in the 1978 mathematics assessment with performance of participants in the 1986 assessment; the same set of items was used on both occasions. The 1978 assessment occurred before MCT were in general use. The better performance of students in 1986 was probably due to the efforts of teachers who made use of MCTs and high-stakes tests. The younger students in 1986 apparently profited more from the MCTs and high-stakes tests than the older students did. It seems reasonable to conclude that the use of MCTs can have desirable influences on performance of young students as measured by the NAEP. Nine tables, including some in an appendix titled "Some Broader NEP Methods and Interests," present study findings. (Contains 16 references.) (SLD)