This study points out the significant role of senior teachers in the process of instruction. It also asserts the consistency and reliability of student assessments of instruction, and the correlation between these assessments and the students' achievement. The study was conducted on groups rather than individual students. The assumption was that when teaching is carried out in groups, it is preferable to relate to the evaluation expressed by the whole group, and its correlation with achievement. The data included 51 student groups studying in 15 departments affiliated with the medical school in 12 hospitals: paediatrics (3), psychiatry (5), gynaecology (4) and surgery (3). The results emphasize the role of senior teachers in the process of instruction. It was found that a high positive correlation exists between senior teachers' direct involvement in teaching and students' academic achievements. However, a low correlation was found between students' assessments of the overall departmental teaching and their academic achievements. Thus, it appears that achievement is not directly influenced by the quality of teaching as perceived by the students, but rather by other factors, with the exception of a positive correlation between the contributions of the department heads to instruction and students' achievement.