This study aimed at investigating the effects of hidden costs of fee-free education on students’ academic attainment in ordinary level secondary schools in Karatu district, Tanzania. The study employed convergent research resign which used both qualitative and quantitative designs. The study was conducted in 14 public secondary schools selected randomly from 31 public secondary schools in the Karatu district. The sample size was 318, consisting of form four students selected using systematic random sampling whereas fourteen parents, fourteen Head of School’s and fourteen Ward Executive Officers were selected using purposive sampling. Data were collected using questionnaires and semi structured interview guide. Quantitative data were analyzed using descriptive statistics while qualitative data were analyzed thematically. The study found that hidden costs had severe effects on students’ academic attainment. Other negative phenomena found to result from hidden costs include truancy and lack of concentration in class. Based on the findings the study concludes that there are serious negative consequences associated with hidden costs and consequently, in free education provision, hidden costs can be counterproductive, potentially able to decrease the chances of attaining the objectives of free education provision. The study recommends that strategies in free education provision should further expand to counterbalance costs of education. Strategies targeted at enhancing general improvements in people’s wellbeing and livelihood are also measures required to enhance the capacity of parents to shoulder the burden of education.