The operational preparations for the Dutch national assessment program in education started in 1986. The program's aim is to periodically describe the contents of the curriculum in use and the attainment of 8-year-old and 11-year-old students on a national basis by means of surveys. In this paper some of the guiding principles in instrument construction, sampling, and data collection are described. The instruments are of two types: (1) questionnaires to make an inventory of the topics actually taught and the variation in the intensity of teaching; and (2) tests to measure the performance of 8-year-old and 11-year-old students in narrowly defined content domains. Data collection will start in 1987 in the field of mathematics. The design for this assessment is described in more detail with special attention to a problem in the application of item response theory in scale construction: the invariance of the location parameters in relation to the opportunity to learn the prerequisite concepts and skills. (Author/JAZ)