This study investigated the influence of truancy and delinquent behaviour on the academic performance of secondary school students in the Federal Capital Territory (FCT), Nigeria. The study adopted a descriptive survey design using a structured questionnaire titled Moral Behaviour and Academic Performance Scale (MBAPS). A total of 300 Senior Secondary II students were randomly selected from nine public secondary schools across Abaji, Gwagwalada, and Kwali Area Councils. Data were analyzed using mean, standard deviation, and t-test statistics at 0.05 level of significance. Findings revealed that truancy and delinquency exert a statistically significant negative influence on students’ academic performance. Students with high truancy tendencies recorded a mean performance score of 52.14 (SD = 6.88), compared with 64.27 (SD = 5.74) for regular attendees (t = 4.72, p < .05). Likewise, students exhibiting delinquent behaviours such as bullying, vandalism, and disobedience to authority had a mean academic score of 49.86 (SD = 7.03), significantly lower than 66.31 (SD = 6.11) for non-delinquent peers (t = 5.09, p < .05). The results confirm that moral decay expressed through truancy and delinquency weakens students’ concentration, classroom participation, and motivation to learn.
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