The aim of this research was to check the effects of teacher's training and teaching methods on academic achievements and interests of students at secondary schools in computer course. The population was divided into four groups; lecture teaching method (control group), discussion teaching method (experimental method), inquiry teaching method (experimental group) and demonstration teaching method (experimental group). Each group has a sample size of 20 students. A pre-test before training of teachers and post-test after training of teachers for academic achievement and interests of students taught by four teaching methods were conducted. The results of pre and post-tests were then analysed by statistical tools of descriptive statistics and ANOVA test. The results of the study indicated that students' academic achievements and interests were increased before and after the training of the teachers taught by lecture, discussion, inquiry and demonstration teaching methods. The demonstration teaching method was ranked 1st and lecture teaching method was ranked last. So, it can be concluded that training of the teacher's plays an important role for choosing the best method for teaching and improves the academic achievements and interests of students.