The goal of this research was to develop and validate an empirical classification of naturally occurring teaching styles in university undergraduate lecture courses. Teaching style was described in terms of patterns of observable classroom teaching behavior.;In the first study, the classification was developed with reference to an initial sample of 298 university lecturers. Each instructor was observed by student raters, who judged the frequency of occurrence of 100 low-inference behaviours. Student ratings were averaged within classes and eight scale scores were computed. A cluster analysis identified six groups of instructors, with members of each group homogeneous in terms of their classroom teaching behaviour patterns. The replicability of the clusters was assessed within this sample through split-half samples, statistical tests, and a comparison of results based on item and scale scores.;In the second study, the typology was validated by investigating relationships between teaching style and other relevant variables, such as instructor characteristics and attitudes, course characteristics, and global student ratings of teaching effectiveness. For this purpose, a second sample of 135 classes was obtained. Significant differences in the frequencies of the six styles across subject area and course level had been noted in the original sample. These differences in style frequencies were replicated in the second sample with regard to course level but not subject area. Overall elevation of the behavioural scale scores played a major role in determining relationships between teaching style and global student ratings. Instructor characteristics such as years of teaching experience, academic rank, and educational goals and attitudes did not display significant relationships with teaching style.;In the third study, additional validation evidence for the typology was gathered through examination of the stability of teaching styles across courses and across years. It was found that behaviour was relatively stable when courses were at the same academic level (i.e., introductory, general, honours), even if the courses were separated by as much as eight years.;In general there was evidence that the empirical classification approach is a useful method for describing teacher behaviour. It allows a definition of teaching style, or educational treatment, in terms of discrete, observable behaviours