Birth Order Effects on Intelligence and Achievement Motivation Among Secondary Students in Adamawa State

This study examines birth order effects on intelligence and achievement motivation among secondary school students in Adamawa State, North East Nigeria. Birth order, reflecting a child's positional rank within the family, has been theorised to influence intellectual development and motivational orientations through resource dilution and tutoring effects. This research adopted a descriptive comparative design involving 380 SS2 students categorised into firstborn, middle-born, and lastborn groups, recruited from nine schools across Yola and Numan. General intelligence was assessed using Raven's Standard Progressive Matrices, and achievement motivation was measured using the Achievement Motivation Scale. One-way ANOVA, post-hoc tests, and regression analyses were applied. Results indicate that firstborn students scored significantly higher on intelligence assessments and reported greater achievement motivation compared to middle-born and lastborn counterparts. However, effect sizes were modest, suggesting that family size, parental education, and socioeconomic status moderated birth order effects considerably. Lastborn children demonstrated higher social motivation and creativity subscale scores, suggesting compensatory developmental advantages. Within larger families of five or more children, birth order effects on intelligence were stronger, consistent with resource dilution theory predictions. The study recommends that parents, counsellors, and educators in Adamawa State avoid treating birth order as a fixed developmental determinant and instead focus on providing equitable stimulation and achievement support to all children regardless of their positional rank. Keywords: birth order, intelligence, achievement motivation, secondary students, Adamawa State.