This study examines the effect of the demonstration method on students' achievement in financial accounting in Gombe state, Nigeria. A sequential explanatory mixed-method design is used where 120 students from six randomly selected schools participated in the study. The students are equally divided into two groups, namely, experimental (i.e., demonstration method) and control group (i.e., conventional approach). Four (4) students participate in the interview. A Financial Accounting Achievement Test (FAAT) is used as an instrument for data collection. The results indicate that at the pre-test stage, there is no significant difference between the achievement of students who are assigned to the demonstration method and that of those who are assigned to the conventional method. The result suggests that the two groups are equal in terms of their achievement at the initial stage. Nonetheless, a significant difference in the financial accounting achievement of students who are exposed to the demonstration method and that of those who are exposed to the conventional method is found at the post-test stage. Specifically, the finding suggests that the demonstration approach is an effective approach to improve the achievement of financial accounting students in secondary school.