In this study we report on a test of a method that uses ontologies to individualize instruction by directly linking assessment results to the delivery of relevant content. Our sample was 2nd Lieutenants undergoing entry-level training on rifle marksmanship. Ontologies are explicit expressions of the concepts in a domain, the links among the concepts, and the governing constraints of these links. We have developed an ontology for the domain of rifle marksmanship. The ontology contains over 160 concepts and over 160 relationships that capture the different types of relations among the concepts (e.g., causal, part-whole, classifying, functional). The content was drawn from Marine field manuals, and interviews with snipers and coaches. Concepts were tagged with instructional content (e.g., definitions, explanations, elaborations, multimedia examples). Relations were tagged with an explanation of why the particular relation holds under particular conditions. Assessment is tied to instruction via influence (Bayesian) networks. Performance on assessment items determines what content is pulled from the ontology for delivery. For example, if a Marine scores poorly on all assessment items related to breathing control, then instructional content tied to the ontology concept "breathing control" (and any linked concepts) could be delivered. Conversely, if a Marine scores low on items that suggest poor knowledge of the shot group associated with poor breathing control, then only a shot group related to breathing might be delivered. Our test of this approach appears feasible and promising. The Bayesian network appeared to be successful in identifying knowledge gaps, and relevant and targeted content was served to Marines. Learning appeared to be occurring at a faster rate over time for Marines who received targeted instruction compared to Marines in a control group. Implications are discussed. (Contains 3 tables and 4 figures.) [The work reported herein was supported under the Office of Naval Research.]