This study examined the effects of heuristic and demonstration methods on senior secondary school students’ academic achievement in mathematics in Adamawa state, Nigeria. The study was guided by three objectives, three research questions and three null hypotheses tested at 0.05level of significance. The population of the study comprises of 34 213 SS II students year 2021 set in Adamawa state from which 311 students were sampled using multistage sampling technique, comprising of 167 male students and 144 female students. Purposive sampling was used to select 6 public schools in Yola North and South Local Government of Adamawa State, while simple random sampling was used to assign intact classes to experimental and control groups. The instrument used for collection of data was Mathematics Achievement Test (MAT). MAT, which is a multiple choice objective test with 50 items, it was drawn from mathematics past questions of West African Examinations Council (WAEC).Data were analysed using Statistical Package for Social Sciences (SPSS) version 16.0. The research questions were answered using descriptive statistics of mean and standard deviation while the hypotheses were tested using both ANCOVA and t-test at 0.05 level of significance. The findings of the study show; (i) a statically significant difference in the mean achievement scores of students taught mathematics using the heuristic method and those taught using the demonstration method as well as lecture method with F-ratio of (145.163) and 𝑝 = 0.00 < 0.05 (ii) statically significant difference between the mean achievement scores of male and female students taught mathematics using heuristic teaching method with t=4.96, p=0.00<0.05. (iii) statically significant difference between the mean achievement scores of male and female students taught mathematics using demonstration method with t=6.378, p=0.00 <0.05. Based on the findings of the study, the following recommendation were made among others: Heuristic teaching method should be adopted by mathematics teachers and should be emphasized more strongly by inspectors from the Ministry of Education. Female students should be paid much attention to in mathematics classroom by organizing extra classes for them using heuristics teaching method.