This study investigated the effect of problem-based learning strategy and feedback on Upper basic II science students’ achievement and cognitive load in Makurdi metropolis, Benue State. The study also tested the effect of problem-based learning strategy and feedback on gender and cognitive load. Seven research questions and seven hypotheses guided the study. A quasi experimental, pretest, post test design was adopted for the study. A total of 116 Upper Basic II students out of 7882 students from three secondary schools in Makurdi metropolis selected by stratified random sampling technique constituted the sample. Two instruments; namely, Basic Science Achievement Test (BSAT) and Cognitive Load Rating Scale (CLRS) developed by the researcher and validated were used for data collection. The reliability coefficient of the instruments were established through a pilot study using Cronbach’s alpha and Spearman Brown prophesy correlation which were found to be 0.81 and 0.80 for BSAT and CLRS respectively. The data collected were analysed using Mean, Standard Deviation, graph, Analysis of Variance (ANOVA), t-test and Analysis of Covariance (ANCOVA). The study revealed that students in the experimental groups achieved significantly higher mean scores than students in the control group in academic achievement in basic science, p = 0.000, p 0.05 and PBL strategy with feedback p = 0.085. The study showed no gender disparity in mean cognitive load when male and female students were exposed to both problem-based learning strategy p = 0.599 > 0.05 and problem-based learning strategy with feedback p = 0.080 > 0.05.. The study revealed that the interaction effect of gender and strategy had no significant effect on both students’ academic achievement p = 0.714 > 0.05 and cognitive load in basic science p = 0.130 > 0.05. Based on these findings the study recommended among other things that Basic science teachers should be encouraged to use problem based learning strategy as a medium of instruction since it improved academic achievement and reduced cognitive load of the students in Basic science
