Increasing numbers of state-mandated testing programs have resulted in the selection of norm-referenced tests (NRTs) for statewide assessment. Adaptation or customization of existing tests has become a viable solution for individual programs. Changes in test instruments have arisen from the behaviorist approach and mastery learning, minimum competency testing, and a cognitive approach. Specific test types arising from each of these concepts are discussed. The national trend has been toward increased involvement of curriculum and instructional personnel in testing. Achievement tests may take varying forms depending on what is to be assessed and the designated outcome. Types of tests available are: (1) shelf NRTs; (2) shelf criterion-referenced tests (CRTs); and (3) customized NRTs or CRTs. Interpretation of test results must always consider that: (1) test equating methods do not mean that interpretation of scores can be the same between a NRT and its customized derivative; (2) content differences occur; (3) individual versus group interpretation varies; and (4) differential instructional effects occur over time. Customized tests provide many benefits but problems of score interpretation must be recognized, as illustrated in a graph. (SLD)