Over a period of about 3 years, 3204 students in Grades 4 to 10 completed 9862 tests to identify and track their interpretation of decimal notation. Analysis of the longitudinal data demonstrates that different misconceptions persist among students to different degrees and in different patterns across the grades. Estimating the prevalence of misconceptions is complex due to the nature of longitudinal data. Best estimates are provided of grade prevalences and the proportions of students affected during schooling. (Contains 1 footnote, 4 figures and 3 tables.) [For complete proceedings, see ED500860.]