The school principal's role in determining the academic achievement of students has been an agenda of controversy among scholars in the field of educational leadership. Several studies, have been carried out, over the years, to resolve this controversy. However, the findings so far have not produced consistent outcomes pointing to the need for further research in differing socio-cultural settings. The main objective of this study was to investigate the relationship between secondary school principals' leadership effectiveness as perceived by secondary school teachers and students' academic achievement West Hararghe Zone, Oromia Regional State, Ethiopia. For this, the study employed correlation design comprising of eight randomly sampled secondary schools. In this study, a total of 190 teachers were selected using a proportional random sampling technique to fill in a standardized questionnaire on the leadership effectiveness of their school principals. Out of 3321 students who sat for Grade 10 national examinations in 2014, the Cumulative Grade Point Average (CGPA) scores of 440 students was selected from the sampled schools using proportional random sampling technique. A standardized questionnaire with five-point Likert scales was used to measure the leadership effectiveness of principals whereas CGPA of students on Grade 10 national examination was used to measure students' academic achievement. The findings of the study showed that the experience of principals was not significantly correlated with their corresponding leadership effectiveness. The findings also showed that the principals level of education was significantly negatively correlated with principals' leadership effectiveness (R = -0.866, p < 0.05). Furthermore, the study findings showed that there was no significant correlation between a school principal's leadership effectiveness and students' academic achievement. The latter finding implies that there was no direct relationship between school leadership and students' academic achievement. In addition, the findings suggest that the relationship between principals' level of education, service year, and leadership effectiveness was not direct. The researchers, therefore, recommended further research on a large scale and in different contexts to come up with more valid and generalizable finding.