This study focuses on competencies of science mentors in assessing student teachers on Applied Science Education (ASE). A total of seventy-six (76) prospective science mentors drawn from one province where the student teachers are also based participated voluntarily during the capacity building mentoring workshops aimed at equipping experienced science teachers with skills on modern practices in science education as well as familiarising them with the training institution’s expectations of students on ASE. The successful candidates were expected to assist university science educators in mentoring and assessment of student teachers. After theory presentations by science educators over two days, trainee mentors were shown two videos of student teachers teaching elementary science classes. They were asked to assess the student teachers using the ASE supervision and assessment instrument designed by the training institution. The plenary session followed where discussions on their assessment were done. The third video was shown to the trainee mentors and it is this video which was used to show any variations of the science mentors from the mean score obtained by the researchers (54%) during their own assessment of the student teacher from the same video. The results show significant inconsistencies of the mentors’ scores ranging from 22% to 84%. The researchers recommend that, it is important to train mentors on the requirements and expectations of the training institution before engaging them and that it is important to have multiple assessments by both mentors and university tutors of students during teaching practice.