To find population proficiency distributions, a two-level hierarchical linear model may be applied to large-scale survey assessments such as the National Assessment of Educational Progress (NAEP). The model and parameter estimation are developed and a simulation was carried out to evaluate parameter recovery. Subsequently, both a hierarchical and a simple model were applied to NAEP reading data. The impact of using a hierarchical model was found to be relatively modest in this case, mostly due to modest clustering. Several other applications and future studies are discussed. (Contains 10 notes and 16 tables.)