International Journal of Education and Research Vol. 2 No. 7 July 2014 675 EFFECTS OF MNEMONIC AND PRIOR KNOWLEDGE INSTRUCTIONAL STRATEGIES ON STUDENTS’ ACHIEVEMENT IN MATHEMATICS Mojeed Kolawole AKINSOLA Department of Teacher Education Faculty of Education, University of Ibadan, Ibadan E-mail: mk.akinsola@mail.ui.edu.ng and akinsolamk@gmail.com and Ezekiel Olukola ODEYEMI Department of Teacher Education Faculty of Education, University of Ibadan, Ibadan All corresponding to the 1 st author. ABSTRACT This study investigated the effects of Mnemonics and Prior Knowledge Instructional Strategies on Students’ achievement in Mathematics. Moderating effects of Numerical Ability and Gender were also examined. The study adopted the pretest-posttest control group, quasi experimental design with 3x2x3 factorial matrix. Two hundred and eighty-eight students from six public schools selected from three local government areas in Ibadan, Oyo State, Nigeria, participated in the study. Two instruments were developed and used: Students’ Mathematics Achievement Test (r=0.75) and Numerical Ability Test (r=0.77). Also used were three operational guides on Mnemonic Instructional Strategy, Prior Knowledge Instructional Strategy and Traditional Teaching Method. Four Null hypotheses were tested at 0.5 significant levels. Data collected was analyzed using Analysis of Covariance, Multiple Classification Analysis (MCA) and Scheffe Post hoc test. The study revealed a significant effect of treatment on students’ achievement in mathematics (F (3, 284) = 8.961, p<0.05). MIS had the higher achievement score of 16.91 than PKIS 13.07 and control group 12.10. Numerical Ability and Gender have significant effect on students achievement in mathematics (F (3,284) = 28.856, p<0.05). Since, MIS and PKIS enhanced students’ achievement in mathematics, therefore, teachers should create mnemonics that link old and new information in the students’ memory, assess their knowledge at the start of instruction through examples that bridge students’ prior knowledge with the new to ensure improved performance and make teaching and learning of mathematics students-centered. Key words: Mnemonic Instructional Strategy, Prior Knowledge Instructional Strategy, Students’ attitude to, Numerical Ability and Gender.