Despite several studies on factors that determine academic performance in public secondary schools with no definite direction, this study examines the influence of school size, its structure and location on the academic performance of students in public senior secondary schools in Lagos State, Nigeria. The study’s foundation hinged on the system theory and adopted Descriptive survey and an ex-post facto design. The study population included the 327 public senior secondary schools and the teachers therein with a sample size of 517 teachers chosen through cluster and simple random sampling from 60 disproportionately selected schools. Data analysis was carried out using both descriptive and inferential statistics of Linear Regression Analysis. The outcome of the data analysis presents that there is a positive and significant influence of school size on academic performance of students of public senior secondary schools in Lagos State, Nigeria ((β = .634, t = 4.335, ρ < 0.05) ; there is a negative and non-significant influence of school structure on academic performance of students in public senior secondary schools in Lagos State, Nigeria ((β = -.022, t = -.119, ρ < 0.05)  while  there is a positive and significant influence of school location on academic performance of students of public senior secondary schools in Lagos State, Nigeria (β = .635, t = 4.336, ρ < 0.05) The study concluded that school building and school structure have  no significant influence on students’ academic performance in public senior secondary schools in Lagos state, The study, therefore, recommended that government should provide more schools as much as possible which will help in decongesting the over-crowded schools and also the united nation’s recommendation of a maximum of thirty students in a class should be strictly adhere to.