Summary Aim. The purpose of this study was to examine age and gender differences in muscular strength and flexibility among primary school children and to compare the findings with data for school-going children from other countries. Method. A cross-sectional survey was conducted among 2 015 primary school children in Makurdi, Nigeria (N.=979 boys; N.=1 036 girls) aged 9-12 years, who performed the FITNESSGRAM (CIAR, 2000) physical fitness tests. Results. A non-significant difference in flexibility was found between boys (mean: 27.1±4.4 cm) and girls (mean: 26.9±4.6 cm) (P=0.851; P>0.05). ANOVA test indicated no significant sex main effect on flexibility test scores (F(1, 2007)=0.027; P>0.05), whereas this yielded a substantial age main effect (F(3, 2007)=3.407; P<0.05). On average, boys had a slight, but significantly superior push-up performance (9.1±3.9) compared to girls (8.6±3.5) (P=0.04; P<0.05). Results also indicated substantial age difference in push-up scores among boys and girls (F(1, 3)=11.1; P<0.05). There were no significant age/ sex interaction effect (F(3, 2007)=1.396; P>0.05) and sex main effect in the sit-up performances for the boys and girls (P=0.188; P>0.05). Boys had significantly (P<0.05) higher mean sit-up values, at ages 10 and 12, whereas no statistically significant sex main effect was found regarding the children’s sit-up scores (F(1, 2007)=1.134; P>0.05). Conclusion. Whereas the study showed non-significant sex and age differences in flexibility between boys and girls, marked age- and gender- related discrepancies were found regarding muscular strength. The muscular endurance component showed inconsistent results across age groups.