Low performance of students in biology has been reported by many researchers. This is attributed to different factors, among which lack of adequate and appropriate instructional materials is one. Instructional materials help both the teacher and the learners in teaching-learning processes. The study investigated the effect of teaching using charts, real specimens and videos on secondary school students’ achievement in mammalian skeletal system concepts. Charts, real specimens and videos were used to teach the experimental groups while lecture method was used to teach the control group. A 4X2 pre-test, post-test quasi-experimental design with control group was used in which a hundred and twenty randomly selected Senior Secondary School II (SSS II) Biology students were drawn from four schools. An instrument developed by the researcher Mammalian Skeletal System Achievement Test (MSAT) was used for data collection. The reliability coefficient of MSAT was 0.796. The data was analyzed using Analysis of Co-variance (ANCOVA) and Scheffe post-hoc test analysis. The findings of this study show that there is significant main effect of treatment on students’ achievement in mammalian skeletal system concepts [F₃^, 111 = 10.489; p< 0.05]. Hence, students performed significantly at different levels in the four groups.  The findings also indicate that there is no significant interaction effect of treatments and gender on students’ achievement in mammalian skeletal system concepts [F₃, 111 = 1.013 p> 0.05]. Real specimens and videos are the best instructional materials that can be used in teaching; they tend to raise the students’ achievement. It is therefore recommended that teachers should develop the technique of integrating different types of instruction materials especially real specimens and videos into their teaching. Educational training programmes should be made available for teachers, which will help to improve their competencies and skills of effective utilization of instructional materials.