Science teachers regularly find themselves confronted with the problem of determining the present level of performance of a student with respect to the course content. Those who approach the assessment of ability and/or achievement within a criterion-referenced measurement framework need to know how accurate and consistent the decision-making procedures are likely to be. In the present study, reliability, validity, and a standards-setting procedure for a criterion-referenced test were examined for use within a science curriculum. The results indicate that there are a number of factors influencing the reliability and validity of the test and that science teachers involved with criterion-referenced measurement need to be aware of these factors to enhance the accuracy of their judgments.