Assessment of student performance is emerging as a crucial ingredient in the recipe for ongoing improvement of school science. This digest focuses on assessment in the service of instruction, for helping students, teachers, and parents monitor learning. According to M. Jorgensen, performance-based assessment requires that the student demonstrate, or perform the actual behavior of interest. Other forms of alternative assessment include concept mapping, journal writing, scoring rubrics to monitor skill development, and the use of portfolios documenting student accomplishments. A first step in considering assessment methods is to become familiar with the wide range of student outcomes that are being endorsed by science teachers, scientists, and the National Research Council. Drawbacks of performance assessments are noted: staff development resources are required, the assessments take more time than conventional methods, standardization is difficult, and the results may not be generalizable from one context to another. (Contains 9 resources and 19 references.) (PR)