The purpose of this paper is to examine the practices of formative assessment in the West Arsi zone secondary schools in Ethiopia. A descriptive cross-sectional survey research design was employed. The study participants were secondary school supervisors, principals, teachers, and students. Questionnaires, interviews, observations, and document analysis were used to gather data. The results revealed that secondary school teachers sometimes communicate learning objectives for students, sometimes integrate formative assessment strategies, and sometimes provide formative feedback, with considerable variation of practices. The results have further shown that lack of instructional materials, absence of laboratory equipment and/or technicians, lack of teachers' competencies, large class size, and shortage of instructional time were the major challenges to formative assessment implementation.