Educational effectiveness research has witnessed some growth in the last three decades because the current era of global competitiveness compels each country to train and equip its citizens with knowledge and skills that would make them successful. Researchers from different countries are investigating factors across various levels within the school system that affect students' learning outcomes and social development. This study applies a multilevel modelling technique (Hierarchical Linear Modeling) on the TIMSS 2011 mathematics data of the Ghanaian Grade 8 students to examine which student-, classroom/teacher- and school-level variables contributed significantly to the performance of Ghanaian students in mathematics. The results indicated that the education system in Ghana is similar to other education systems where the students' academic achievement is correlated with a set of students, classroom/teacher and school characteristics. However, unlike other educational systems, the findings of the current study suggested that the difference in students' achievement in mathematics is mainly due to school factors. It was concluded that the poor performance of Ghanaian students in mathematics is at least partially attributable to inadequate preparation of teachers, emphasis on lower rather than higher thinking skills, inconsistent use of homework, failure to engage students in their learning, lack of progress of girls, lack of students' interest and confidence in mathematics and students' lower educational aspiration.