Large-scale assessment results for schools, school boards/districts, and entire provinces or states are commonly reported as the percentage of students achieving a standard--that is, the percentage of students scoring above the cut score that defines the standard on the assessment scale. Recent research has shown that this method of reporting is sensitive to small changes in the cut score, especially when comparing results across years or between groups. This study builds on that work, investigating the effects of reporting group size on the stability of results. In Part 1 of this study, Grade 6 students' results on Ontario's 2008 and 2009 Junior Assessments of Reading, Writing and Mathematics were compared, by school, for different sizes of schools. In Part 2, samples of students' results on the 2009 assessment were randomly drawn and compared, for 10 group sizes, to estimate the variability in results due to sampling error. The results showed that the percentage of students above a cut score (PAC) was unstable for small schools and small randomly drawn groups.