Education is considered a vital cog in a country’s economic engine in terms of training, research and development. Accordingly, a formal education system remains a mode of rationing opportunities, differentiation and the allocation of individuals into various positions within a society’s social stratification structure. Certainly, the obtainment of educational credentials has been linked to occupational, trajectory, income, and attendant life chances. In light of this, the achievement gap remains an important issue since an education provided in a more equal and equitable manner could be an important tool to bridge the gap between the rich and poor citizens within a country. This study aimed to ascertain the Matthew effect and its contribution to students’ academic achievement gap in the basic education schools of Rwanda. The study was guided by descriptive and correlational research design, stratified and systematic random sampling as well as purposive sampling were used to select 350 participants, including 51.4% males and 48.6% females, mostly aged 30 to 40 years. Quantitative and qualitative data were collected through questionnaire and interviews. The collected data were descriptively analysed using IBM-SPSS 21. The study established that socio-economically disadvantaged students mostly enrol in under-resourced and low-performing schools i.e. public and government-aided schools. Furthermore, the study identified that private and international school students outperform their counterparts enrolled in public or government-aided schools. Moreover, a significant (p-value .011) low degree of positive correlation (r= .159) was established between the students’ academic achievement and their parents’ socio-economic category. In conclusion, the Rwandan aim of ensuring access to quality, equitable and effective education for all is facing a bleak foreseeable future due to the existing academic achievement gap influenced by the Matthew effect. Recommendations were therefore formulated with a view to eradicating the Matthew effect in the basic education schools of Rwanda.