This study investigated the effect of conceptual-demonstration strategy on interest, retention and performance in geometry among Junior Secondary Students. The study adopted quasi-experimental design involving pretest, posttest and postposttest using one experimental and one control groups. A pretest was administered before the treatment to establish the equivalence of the experimental and control groups. Four junior secondary schools with a population of 212 students were randomly selected. The sample was divided into two groups Experimental and Control Groups namely;GSS Pambegua, GGSS Kawo, GSS Bomo and GGC Kwoi with 109 male and 103 female students as experimental and control respectively. The effectiveness of conceptual-demonstration strategy with experimental classes was compared with the effectiveness of the conventional method of teaching geometry in the control classes. Geometry Performance Test(GPT), Geometry Retention Test (GRT) and Geometry Interest Scale (GIS) data were analysed to determine the effectiveness of the two instructional strategies and the three research questions and hypotheses were tested using Means, Medians, Standard Deviation, T-Test Analysis and Mann-Whitney reliability coefficient of p≤ 0.05. The results showed that students taught using conceptual-demonstration teaching strategyperformed significantly higher in geometry test than their counterparts exposed to conventional method of teaching. The researcher recommends among others for the improvisation of conceptual-demonstration teaching strategy within the context of mathematics teaching in junior secondary schools and the mathematics teachers should continue to use and adopt conceptual-demonstration teaching strategy more into strain of their classroom practice.