The study investigated a constructivist instructional strategy and pupils’ achievement in and attitude towards primary science. The population was 650 Basic-5 pupils in 21 public primary schools in Western Senatorial District of Rivers State, Nigeria. The sample of 180 pupils was drawn from four intact classes from four schools in the area. Primary Science Achievement Test (PAST) and Primary Science Attitude Scale (PSAS) were the instruments used for the study. Test-retest reliability coefficient and Cronbach alpha 21 reliability was 0.82 for PSAT and 0.85 for PSAS, respectively. Four research questions and four corresponding null hypotheses guided the study. Analysis of covariance (ANCOVA) and multiple classification analysis (MCA) were used in analyzing the data. Results showed that the constructivist strategy was more effective than expository strategy in facilitating pupils’ achievement in and attitude towards primary science. Pupils’ from urban schools performed significantly better than pupils from rural schools under each of the two methods. The researchers advocated for the use of constructivist strategy by primary science teachers among their recommendations.