ABSTRACT
We begin with two fundamental and complementary propositions. First, you cannot assess everything. Second, not everything is worth assessing. As a consequence, the first step in designing an instrument to assess student achievement is to determine what is worth assessing. To make this determination teachers would be wise to focus on what may be termed a curriculum unit or unit of instruction. Whatever terminology is used, a unit is a series of lessons related to a single topic or cluster of objectives. Typically units require from 2 to 3 weeks to complete (although some are longer).
