The study of federal education initiatives that takes place over multiple years in multiple settings often calls for aggregating and comparing data-in particular, student achievement data-across a broad set of schools, districts, and states. The need to track the trends over time is complicated by the fact that the data from the different schools, districts, and states also may have been based on different achievement tests. This article suggests one approach for defining a common metric: calculating the standardized slope of a time series of datapoints. The standardized slope serves as an effect size statistic. Meta-analytic techniques can be employed because the student achievement test results from different states can therefore be considered equivalent to the findings from different studies.