1 EFFECT OF PROBLEM-BASED LEARNING METHOD ON PUPILS’ ACHIEVEMENT AND RETENTION IN MATHEMATICS IN ORUMBA SOUTH LOCAL GOVERNMENT EDUCATION AUTHORITY, ANAMBRA STATE Ijeoma A. Okoli¹; Faith E. Anyachebelu² & Joy O. Enemuo³ 1,2&3 Department of Early Childhood and Primary Education, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria Corresponding Author: Ijeoma A. Okoli, Department of Early Childhood and Primary Education, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria ABSTRACT This study investigated the effect of Problem-Based Learning Method (PBLM) on pupils' academic achievement and retention in Mathematics in Orumba South Local Government Education Authority. Four research questions guided the study and six hypotheses were tested at 0.5 level of significance. The study adopted a quasi-experimental research design. The population of the study comprised 973 basic 5 pupils in the 43 public primary schools in the study area. 64 pupils formed the sample size which was selected using multi stage sampling procedure. The instrument for data collection was Pupils Everyday Statistics Achievement Test (PESAT). The instrument was validated by three experts. The reliability coefficient of 0.72 was established for PESAT using Kudar Richardson's formula 20 (KR-20).Mean and standard deviation were used to answer the research questions. Analysis of Covariance (ANCOVA) was used to test the null hypotheses. The findings of the study revealed that Problem-Based Learning Method (PBLM) is more effective in enhancing pupils' achievement and retention in Mathematics than the conventional expository method. There was no significant difference in the achievement and retention in mathematics due to gender. Also, there was interaction effect of teaching methods and gender on pupils' achievement and retention in mathematics. Based on the findings, it was recommended among others that PBLM be adopted by mathematics teachers to optimize learning outcomes for all pupils. Keywords: Achievement, Mathematics, Problem-Based Learning Method, Retention,