This study investigated the effectiveness of implementing the Jolly Phonics strategy on pupils’ reading achievement and attitude within the context of lower basic schools in Lagos State, Nigeria. Two research questions and two hypotheses guided the study. The study adopted the quasi-experimental pre-testing, post-test, control group experimental design. The population of the study consisted of all basic 1 pupil in public lower basic schools in Lagos State. While the sample size was Three hundred and twenty-four (324) pupils of Lower Basic 1 and Nine (9) teachers who were randomly and purposively selected using Simple Random sampling technique. The sample size was drawn from three schools from three Local Government Education Authority Areas (LGEAs) in Lagos State public lower basic schools. Two research questions were used and three instruments used for eliciting responses were Achievement Test in Reading (ATR), Pupils’ Attitude to Reading Questionnaire (PARQ) and Pupils’ Verbal Ability Test (PVAT). The instruments were validated by experts in early childhood and measurement and evaluation. The test re-test method was adopted for instrument reliability at 0.75. The data collected were analyzed using descriptive statistics (Mean and Standard deviation) Variance and Analysis Covariance (ANCOVA) Findings revealed that Jolly Phonics had significant effect on the academic achievement in reading of basic 1 pupil in lower basic schools and their attitude. Pupils taught with Jolly Phonics strategy performed better in reading achievement and had positive attitude than those taught with conventional method. It was recommended that Jolly phonics instructional strategies should be incorporated into basic school reading curriculum. This will help them develop reading skills easily. Individual differences in pupils’ reading ability should be identified and addressed through variation of reading strategies as was provided for in the experimental groups with jolly phonics strategy. Government, school managers and administrators should provide adequate instructional materials that will motivate pupils to easily adapt to jolly instructional strategy.