Educational authorities in Ghana have generally established that the performance of school leavers especially at the pre-university level offered a large room for improvement, due to so many factors. Hence, the introduction of the New Educational Reform in 1987 which led to the new system of Senior Secondary School with the first product in 1993. The study was to create awareness of whether Ghana's New Educational Reform, which has been in place since 1987, has led to improvement in performance of Senior Secondary Schools in Ghana in the area of the four core disciplines: Mathematics, Integrated Sciences, Social Studies, and English language. Two way Analysis of Variance (ANOVA) without replication was derived to determine whether significant differences existed between grades, subjects and the years involved in the study to obtain some dimensions for determining the performance of students in the institution. Social Studies and the grades C, D and E gave the institution a glorious image while Mathematics, Integrated Science and English Language and grade F, gave the institution a poor image. However, majority of the grades A and B were associated with Core Mathematics. There was no significant difference in the trend of students' performance between years in the study period. We recommend that future research spanning a period from 2006 to 2014, which has different grading system, under the West African Senior School Certificate Examination (WASSCE) grading system, be done in a comparative manner. This might include students in two or three regions of Ghana. To make the research generalizable, random samples of schools and students must be considered.