ABSTRACT
This study investigated effects of instructional materials on the academic achievement and retention of SS 2 biology students in Delta State. The study sample consisted of 86 SS2 biology students randomly selected from a population of 5,626 students drawn from 18 public schools. An instrument designed and developed from past WAEC questions by the researcher known as Biology Achievement Test (BAT) was validated by some senior lecturers in science, English and statistic from Ahmadu Bello University and senior biology teachers in Delta State. The instrument used was tested and certified to be reliable at 0.65 coefficient. Quasi-experimental design was adopted which involves two groups: experimental and control groups. The experimental group was subjected to treatment using instructional materials but the control group was taught without any instructional materials. Four null hypotheses were tested using t-test statistics. The following major findings were made: There is a significant difference between the mean academic achievement scores of students taught using instructional materials (EG) and those taught without the use of instructional materials (CG).There is no significant difference in the mean achievement scores of male and female students taught biology concepts using instructional materials. There is significant difference in the mean retention scores of students taught with instructional materials and those taught without instructional materials. There is significant difference in the retention ability of male and female students exposed to the use of instructional materials. On the basis of these findings some recommendations were made, one of which is teachers should make use of instructional materials to facilitate the teaching of biology at secondary school level.