Tasks are the most visible element in an educational assessment.
This paper concerns issues in assessment design that must be addressed for assessment tasks to serve this purpose effectively and efficiently. The first part of the paper describes a conceptual framework for assessment design, which includes models for tasks. Coherent design requires that these models be coordinated to serve the assessment's purpose. The second part of the paper focuses attention on the task model. It discusses the several roles that task model variables play to achieve the needed coordination in the design phase of an assessment, and to structure task creation and inference in the operational phase.