A number of states have school building accountability systems that rely on comparisons of achievement from one year to the next. Improvement of the performance of schools is judged by changes in the achievement of successive groups of students. Year-to-year changes in scores for successive groups of students have a great deal of volatility. The uncertainty in the scores is the result of measurement and sampling error and nonpersistent factors that affect scores in one year but not the next. The level of uncertainty was investigated using fourth-grade reading results for 4 years of administration of the Colorado Student Assessment Program. Results were available for between 700 and 800 schools each year. It was found that the year-to-year changes are quite unstable, resulting in a near-zero correlation of the school gains from years 1 to 2 with those from years 3 to 45. Some suggestions for minimizing volatility in change indices for schools are provided. (Author/SLD)