Online-ISSN 2411-2933, Print-ISSN 2411-3123 June 2016 International Educative Research Foundation and Publisher © 2016 pg. 34 Improving Secondary School Students’ Achievement In English Essay Writing Using Two Modes Of Essay Structure-Based Instructional Strategies Ezeokoli, F.O. Ph. D. drezeokoli@yahoo.com Department of Teacher Education, University of Ibadan, Ibadan, Nigeria Igubor Patience Department of Curriculum and Instructional Technology, University of Benin, Benin City, Nigeria Abstract Writing is a tool for communication and learning.However, students’ performance in essay writing in Nigeria has been poor. This under-achievement has been traced to ineffective methods and strategies. Literature reveals that most studies focused on innovative ways to improve students’ achievement in essay writing without attention to essay structure-based instructional strategies. This study, therefore, determined the effects of two modes of Essay Structure-Based Instructional Strategies (ESBIS) on students’ achievement in argumentative and expository (cause/effect) essays. The moderating effects of vocabulary knowledge and attitude to essay writing were also examined. The study adopted a pretest-posttest, control group, quasi-experimental design using a 3×2×3 factorial matrix. Two Local Government Areas (LGAs) in Benin City were randomly selected. Three public secondary schools from each LGA were purposively selected while two intact SS II classes were randomly assigned to each of the treatment and control groups. The instruments used include: Achievement Testsin Argumentative (r=.79) and Expository Essays (r=.80), Vocabulary Knowledge Test (r=.83), Questionnaire on Students’ Attitude to Essay Writing (r=.73). Data were analysed using ANCOVA and Bonferroni post-hoc test at 0.05 alpha level.There was significant main effect of treatment on students’ achievement in each of argumentative (F (2, 284) = 9.78; .064) and expository (F (2, 284) = 55.26; .28) essays and in both combined (F (2, 284) = 4.80; .033). The two-way interaction effect of treatment and the moderator variables on students’ achievement in each of argumentative and expository essays as well as in both combined was not significant. Keywords: Essay structure-based instructional strategy; Attitude to essay writing; Vocabulary knowledge; Achievement in essay writing