Although scientific and technological developments are mathematics-based, many students continue to perform poorly in mathematics. This study investigated how students' mathematics self-concept (MSC) is related to their motivation to learn mathematics (SMOT) and gender differences in the two constructs. Out of 165,900 students in 256 secondary schools, 649 students in 32 randomly selected schools completed a validated, group-administered questionnaire whose [alpha]-reliability was 0.88 and 0.89 for MSC and SMOT, respectively. Results, at 0.05 [alpha]-level, show a statistically significant relationship between students' MSC and SMOT. MSC explained 63% of the variance in SMOT. Gender differences, favoring boys, in students' MSC and SMOT were significant with girls in co-educational schools being the most disadvantaged. The study concludes that students' MSC is related to SMOT and is differentiated by gender, grade level and school's social set up, and that boys perceive their success in mathematics more positively than girls. It recommends that educators enhance students' MSC and SMOT through regular feedback, using a variety of instructional approaches and media, creating students' interest in mathematics, making it relevant and increasing students' probability of success and satisfaction. Educators should introduce positive interventions in form 1 and should conduct further research to determine why girls, more than boys, detest learning mathematics.