This study examined the effect of training in math metacognition on fractional mathematics among primary school pupils, with a quasi-experimental design, specifically a post-test only control group design. Two intact classes were randomly selected and assigned to treatment and control conditions. Sixty primary six pupils constituted the sample size. Two research questions and three null hypotheses guided the study. A FAT (Fraction Achievement Test) was developed, validated and used for data collection. The data collected were analyzed using mean, SD (standard deviation) and ANOVA (analysis of variance). The result of the study showed that training in math metacognitive strategy improved pupils' achievement in fractional mathematics. The study also showed a significant gender difference in the achievement of pupils in fractional mathematics. Hence, a good understanding of fractions is requisite to excellence in school mathematics; the study recommends that training in math metacognitive strategy should be urgently introduced in teacher preparation in order to remedy the prevalent mathematics fear and failure in Nigeria. (Contains 2 tables.)