The research was designed to investigate the effect of content-based instructional method on secondary school students’ achievement in English language composition writing in Kogi State. Gender and school location were important variables considered in the study. Three research questions and three null hypotheses guided the study. A quasi-experimental research design (pretest, posttest and control group) was adopted by the researcher for the study. The sample of the study was intact classes made up of 299 SS2 students. Extraneous variables were controlled in the study. An essay topic was given to the students. The co-efficient of reliability was 0.88 using Kendall’s Coefficient of concordance (w). The data collected from the study were analysed using analysis of covariance (ANCOVA). The major findings of the study were that content-based instructional method improved students’ academic achievement unlike the conventional method; female students achieved higher, than male students in English language composition; students in urban area achieved higher than their counterparts in rural areas in English language composition writing. Based on the findings, it was recommended, among others, that content-based instructional method of teaching should be included in all the teacher education programmes This will create awareness on the rest of the teachers of English language and help to enhance the academic achievement of the students in English language composition writing which impacts positively on the teaching and learning of English language in general.