This study explored the impact of learner-instructor-interaction and conventional lecture methods on students’ academic performance in basic science in junior secondary schools in Lagos State Education District V, Nigeria. A non-randomized pre-test, post-test, non-equivalent quasi-experimental research design in two intact classes which comprised of 117 students with 50 in experimental group and 67 in control group from two randomly selected junior secondary schools in Amuwo-Odofin zone of the district was used. While students in the control group completed course assignments individually, students in the treatment group completed the assignments in small groups which enable effective students-instructor-interaction. Students’ Academic Performance Test (PAPT) and Students’ Attitude Questionnaire (SAQ) which were validated by two experts in science education with reliability of 0.79 and 0.87 were used for data collection. Analysis of Covariate (ANCOVA) was used to analyze the null hypotheses at 0.05 level of significant. The results of the study revealed that learner-instructor has a statistically significant effect on students’ academic performances [F(1,115)=14.16; p<0.05; ɳ2=0.54]. Students working collaboratively achieved significantly higher than those working individually. Finding also shows that student-instructor fostered a statistically significant positive attitude among learners [F(1,115)=0.58; p<0.05; ɳ2=0.41]. Further finding revealed no statistically significant effect of learner-instructor interaction on students’ academic performance and attitude based on school type. According to the study’s findings, it is advised, among other things, that learners should be taught utilizing the three-tier system of instruction in order to improve their knowledge in terms of students’ learning results. The study concluded that learner-instructor-interaction had an impact on students’ academic performances to retention. These shows that students ‘academic performance is improved through learner-instructor interaction. This study recommends among others that, students should be taught through learner-instructor interaction in order to promote academic performance.