This study observed the effects of school plant organization on instructional efficiency and performance of students in Osun State public secondary schools. It employed a quantitative research design of correlation type. The study sampled 100 public secondary schools in the three senatorial districts of the state using systematic random sampling method. A researcher- designed questionnaire titled 'School Plant Organization and Instructional Efficiency Questionnaire" (SPOIEQ) was used to collect data on relative location of school plant facilities in the schools. The construct and content validity of the instrument was done by experts in research. The question items were reviewed by the specialists and corrections were affected as suggested by them. After a test-retest treatment within two weeks interval, the scale recorded a cronbach alpha of 0.75. The study found out that most specialized school plant facilities (laboratories, libraries, playgrounds, workshops, hostels and staff offices) were located considerable distance from the classrooms thus requiring longer mean time for teachers and students to move into or from them for teaching and learning. Also, a significant relationship was established between school plant, instructional efficiency and academic performance with F- value (0.36) > critical Fvalue (0.19) at 0.05 level of significance. School plant organization and student attendance/ punctuality at lessons were found to be significantly related with F-value (0.7921) > critical Fvalue (0.16) at .05 level of significance. School plant organization and teachers attendance/ lesson completion was found to be significantly related with F-value (0.5500) > critical F- value (0.16) at 0.05 level of significance. The study concluded that school plant location have a role to play on the effectiveness of instruction and the ultimate performance of students in their examinations. It thus recommended the construction of 'Integrated Classrooms' that can house almost all teaching activities under one big roof.