In teacher education the integration of theory and practice is extensively debated. Empirical evidence, however, is scarce. Therefore, this study presents a test tapping teacher candidates' theoretical knowledge about learning, development, and assessment. Based on an empirically defined content, 101 items were developed and administered to 3298 teacher candidates after university teacher education. After specifying a suitable item response model, structural analyses reveal that the predefined 3-dimensional provides reliable test scores. After controlling for individual characteristics, persons without university teacher education obtain lower scores for learning and development, which adds further validity evidence. Within a longitudinal design, knowledge predicts changes in instructional behavior. The results are discussed concerning future research on the interplay of theory and practice in teacher education.