The study analysed the success factors of high-achieving secondary schools selected from Kinondoni District in Dares-salaam region. Specifically, the study sought to: identify the characteristics of students of high-achieving secondary schools that influence their academic achievement; determine the contribution of teachers on students’ academic achievement, identify the role of heads of schools on student academic achievement; and to determine parental role in promoting academic performance of their children. Mixed research methods approach was employed while data were gathered through questionnaires, interviews, and documentary review. The target population consisted of 5 heads of schools, 5 academic teachers, 40 teachers and 65 students from the 5 selected secondary schools leading to a sample size of 115 respondents. Purposive sampling was used to select heads of schools and academic teachers. The qualitative data was analyzed using thematic analysis while quantitative data from students’ and teachers’ questionnaires were analyzed using simple descriptive statistics with the aid of the SPSS programme. The reliability of instruments was tested through Cronbach Alpha scale yielding reliability coefficient of 0.758. The validity of the instruments was established through consulting several experts. The study revealed that there is a link between students’ characteristics and academic achievement. The findings also showed that high-achieving schools are staffed with teachers who have high expectations for all students. Furthermore, the study revealed that parents’ involvement in the education of their children contributes to academic achievement in high-achieving schools. Basing on the findings of the study it is recommended that, students should be shaped by inflicting in them a set of core values including respect, honesty, courage, and responsibility that could make learning effective. Likewise, the study recommended that teachers and head of schools should be trained so as to help them gain the required knowledge and skills.