This study traces the development of a vocabulary measure designed to assess multiple types of word knowledge. The assessment, which was administered in conjunction with a science unit about weather and the water cycle for third-and-fourth graders, included items for six knowledge types--recognition, definition, classification/example, context, application, and interrelatedness. The model that included the full range of items provided a better fit with the construct vocabulary knowledge than did the model that included only the definitional knowledge most often assessed in traditional measures. This study provides preliminary support for the feasibility of a multidimensional vocabulary assessment.