The study investigated the Effect of Keller System of Instruction (KSI) on students’
Achievement in Biology. The design of the study was a quasi-experimental, nonequivalent pretest and posttest control group design. 7,612 Senior Secondary School one (SSS1) biology students in Abakaliki Education Zone of Ebonyi State formed the population of the study. A sample of three hundred and thirty-two (332) students from intact classes of four schools was used for the study. Four co-educational secondary schools in Abakaliki Education were purposively sampled for the study. Two schools were randomly assigned to the control group while the remaining two schools were assigned to the experimental group. The experimental group was taught biology with KSI while the control group was taught with the traditional method. The instrument used to collect data for the study was Biology Achievement Test (BAT). The instrument was face validated by experts in biology education, and measurement and evaluation. The reliability of BAT was determined using the Kuder-Richardson formula (KR-20) and a Reliability index of 0.80 was obtained. The instrument was also subjected to estimation of stability using a testretest procedure. The stability coefficient obtained for BAT was 0.95. The data obtained from the study were analyzed using mean and standard deviation for answering research questions while (ANCOVA) was used for testing the hypotheses. The findings of the study revealed among others that: Keller System of Instruction (KSI) was significantly better than the conventional teaching method in enhancing students’ achievement in biology; there was no significant interaction between gender and teaching method on students’ achievement in biology. Based on the above findings, recommendations were made which include biology teachers should introduce KSI in their lessons to enhance students’ achievement in biology; and educational trainings, workshops and conferences should be organized where the teachers could be sensitized on the efficacy of KSI in enhancing the students’ achievement in biology.

Keywords: Achievement, Keller System of Instruction, Conventional Method of
Teaching, Biology