We propose the concept of cultural validity as a form of test validity in science assessment. The conceptual relevance of cultural validity is supported by evidence that culture and society shape an individual's mind and thinking. To attain cultural validity, the process of assessment development must consider how the sociocultural context in which students live influences the ways in which they make sense of science items and the ways in which they solve them. These sociocultural influences include the values, beliefs, experiences, communication patterns, teaching and learning styles, and epistemologies inherent in the students' cultural backgrounds, as well as the socioeconomic conditions prevailing in their cultural groups. We contend that current approaches to handling student diversity in assessment (e.g., adapting or translating tests, providing assessment accommodations, estimating test cultural bias) are limited and lack sociocultural perspective. We find that attaining cultural validity may conflict with current basic principles and assumptions in testing, such as item independence and standardization. We discuss the ways in which adopting cultural validity as a criterion for test validity makes it necessary to shift assessment paradigms and adopt new procedures for assessment development. © 2001 John Wiley & Sons, Inc. J Res Sci Teach 38: 553–573, 2001