This study proposed a model for the washback effect of a high-stakes test in Ghanaian Senior High Schools. The proposed model focused on the micro washback effect of a high-stakes test, as the washback effect is multidimensional. The study reviewed Hughes', Bailey's, and Nguyen's washback effect models of a high-stakes test. The assumption that underpinned the proposed model was that the washback effect of a high-stakes test is inevitable, and it will affect teachers’ classroom instructional practices, implementation of the syllabus, and students’ learning practices. It was concluded that in the classroom context, a high-stakes test could have either a positive or negative effect on classroom instructional practices, implementation of the syllabus, and students’ learning practices.