The author deals with one aspect of the methodological contrast between open ended discovery teaching and the direct instructional sequence used by the expository teacher; namely the prevailing style of verbal interaction between teacher and students. Among other factors which the results of research have indicated may be important in determining student achievement in science are: (i) teacher's qualifications and years of teaching experience; (ii) students' intellectual style as measured by IQ scores; (iii) social status of students; (iv) type of school and the area it serves; (v) number of students in class; (vi) level of provision of apparatus, textbooks etc; (vii) time allocated to science.