Many states have implemented high-stakes testing since the enactment of the No Child Left Behind Act of 2001. Yet the question remains whether high-stakes tests effectively measure student proficiency. This report describes a study that compared results on high-stakes tests with results on other standardized tests not used for accountability purposes and thus considered low-stakes tests. Data for the comparisons were gathered from test scores from 5,587 schools in 9 school systems in 8 states. Scores were compared on each test given in the same subject in the same school year. When possible, the results of high-stakes and low-stakes tests given at the same grade levels were also compared. For all the school systems examined in the study, high correlations between score levels on high-stakes and low-stakes tests were found. Also found were some high correlations for year-to-year gains in scores on high-stakes and low-stakes tests. But the correlations of score gains were not as consistently high, and in some places were quite low. The report concludes that stakes of the tests do not distort information about the general level at which students are performing. (Contains 10 tables and 23 references.) (WFA)