The purpose of this study was to find out the effects of truancy on academic achievement among pupils in public primary schools in Kenya. The study would assist teachers on specialized intervention methods so that they can have knowledge on how to intervene on truant behaviour in primary schools. Teachers and pupils in Nairobi County were interrogated about the causes and factors that lead to pupil’s truancy. Questionnaires and interview methods were used to collect data from teachers and pupils. The findings indicated that truancy affected enormously the academic achievement of learners and further, the study showed that learners from poorer zones of Nairobi County had high numbers of truancy than schools from well to be zones. There was also gender discrepancy where by truant behaviour was found to have affected more boys than girls in the different social class schools. What the teachers revealed indicated that truancy in Nairobi County could be prevented if there were policies put in place by the government on workable solutions to assist learners. They further indicated that various programs could attract learners stop truant behaviour. Such programs included sports and feeding programs which were highly recommendable. Truancy affected pupils from an early time of school attendance and therefore it is recommendable a multifaceted approach be considered therefore early intervention was found to be useful.