Identifying the factor structure of online reading to learn is important for the development of theory, assessment, and instruction. Traditional comprehension models have been developed from, and for, offline reading. This study used online reading to determine an optimal factor structure for modeling online research and comprehension among 426 sixth graders (ages 12 and 13). Confirmatory factor analysis was employed to evaluate an assessment of online research and comprehension based on a widely referenced theoretical model. Student performance reflected the theoretical constructs of the model, but several additional constructs appeared, resulting in a six-factor model: (a) locating information with a search engine, (b) questioning credibility of information, (c) confirming credibility of information, (d) identifying main ideas from a single online resource, (e) synthesizing information across multiple online resources, and (f) communicating a justified, source-based position. The findings are discussed in terms of theory, assessment, and instruction.