Ogunleye, B. O. (2019). Effects of concrete-representational-abstract instructional strategy on chemistry performance of students with mathematics learning difficulties in Ogun State, Nigeria. Kampala International University Journal of Education,14(2):135-151. Effect of Concrete-Representational-Abstract Instructional Strategy on Chemistry Performance of Students with Mathematics Learning Difficulties By Dr. Bamikole O. Ogunleye National Open University of Nigeria Victoria Island, Lagos +234-8034072263 bogunleye@noun.edu.ng Abstract Science and technology has great roles to play in the contemporary society and is persistently affecting our daily lives and activities already. Over the years, students’ performance in science subjects especially chemistry have continued to depend on Mathematical knowledge. This is so because chemistry houses a good number of concepts and principles which are either mathematical or mathematics-based. Further, recent West African Examinations Council’s Examiners Reports revealed students’ poor performance in aspects that require mathematical computations in the Senior School Certificate Examinations in Nigeria. This study, therefore, determined the effect of Concrete- Representational-Abstract Instructional Strategy (CRAIS) on students’ achievement in Chemistry. The pretest, posttest, control group quasi - experimental design was adopted. A total of one hundred and sixty-eight SSII Chemistry students with Mathematics Learning Difficulties (MLD) from four schools participated in the 6-week study. Instructional Guides for CRAIS and conventional instruction as well as Mathematics Learning Difficulties Test (r=.85) and Students’ Chemistry Achievement Test (r=.88) were used. Data collected were analysed using Analysis of Covariance with pretest scores as covariates. The CRAIS was found more effective (x  =14.51) than the control group (x  =12.10) significantly (F (1,167) = 6.86; p<.05). The CRAIS was, therefore, recommended for teaching mathematical aspects of Chemistry especially to students with mathematics learning difficulties. Key Words: Concrete–Representational-Abstract, Instructional Strategy, Chemistry, Mathematics Learning Difficulties. Introduction The importance of science and technology in contemporary society is demonstrated by its conscious and unconscious use in our daily lives. Indeed, transportation, electrical devices, medicine and food are benefits of science and technology. Also, modern societies are literally built on Science and Technology. Opara (2004) states that science and technology have long been recognized as the instrument par excellence for nation building. This is why greater emphasis is being placed on industrial and technological development not only in Nigeria but the world over. Science, Technology and Mathematics (STM) education plays a dominant role in