school students in mathematics: the school type perspective. Background: When the scoring pattern is guided, it is likely to result in uniformity of scoring of students’ work and involvement of students in their own assessment. GSIS may or may not have effect on the school type, since schools are usually either for female only, male only or mixed (coeducational). Aims: The study specifically sought to find out the effects of the GSIS on students based on school type. Methods: The design of the study was quasi-experimental, utilizing pre-test, post-test groups. A sample of 336 senior secondary class one students were chosen from a population of 3,111 from three (3) school types in Owerri municipal council, Imo State, Nigeria. The simple random sampling technique was used for selecting the experimental students while purposive sampling technique was used for selecting the 3 experimental schools. One research question and four hypotheses guided the study. Data obtained from pre-test and post-test were statistically analyzed using mean and analysis of covariance (ANCOVA). Results: The results showed that there was difference in the effects of guided scoring instructional strategy (GSIS) on students in different school types with female school having the highest effect. Conclusion: School type is a factor in students’ achievement with GSIS. The strategy was recommended to be used in all school types to enhance secondary school teaching and learning outcomes