Research on learning styles and their assessment has been the focus of growing interest due to rapid advances in educational multimedia applications. As an alternative to conventional questionnaires, the VV-BOS, a computer-based instrument for direct observation of students' preference for visual or verbal learning material in an authentic learning situation, was developed. A study with 103 second language learners was conducted to assess the reliability and validity of the scale scores provided by this instrument. The visualizer/verbalizer scale scores were highly reliable. They correlated moderately with corresponding VVQ and ELSIE questionnaire scale scores. Students' learning outcome could successfully be predicted using the VV-BOS scale, but not using the questionnaire scales. The results indicate that the direct observation of students' preferential choice behavior is a promising alternative to conventional questionnaires for the assessment of individual differences in multimedia training and instruction.