Four factors essential to determining how many items should be constructed or sampled for a set of objectives are examined: (1) importance and type of decisions to be made with the results; (2) importance and emphases assigned to the instructional and behavioral objectives; (3) number of objectives; (4) practical constraints, such as item writing time, time available to administer the test, and student characteristics. Within the context of related research on cut-off scores and reliability, it is recommended that between 5 and 10 items per objective be employed for most classroom decisions and between 10 and 20 items be used for school, system, and state level decisions. Specific guidelines for teachers and evaluators, and an illustrative application using objectives from a second grade dictionary skills unit are provided. (Author/MH)