U.S. public schools play a central role in identifying student disabilities. Using administrative data, we examine how third-grade class rank affects subsequent disability classification, leveraging variation in school-cohort achievement distributions to isolate rank from students' own achievement. Students in the lowest ventile are 3.8 percentage points more likely to be classified as having a disability than students at the median (10\textsuperscript{th} ventile). Students at ventiles above the median exhibit smaller but statistically significant estimated increases relative to the median as well. These patterns are driven primarily by classifications of learning disabilities and health conditions such as Attention-Deficit/Hyperactivity Disorder (ADHD). We further document that low-ranked students are more likely to receive a testing accommodation in fourth grade. Together, these findings highlight the role of subjective factors in shaping disability diagnoses and the allocation of testing accommodations.