This study was designed to investigate the effect of target task approach on students’ achievement in senior school chemistry. Two research questions and three null hypotheses guided the study. The design of the study was a pretest- post- test non- equivalent control group design. A total of one hundred and sixty (160) senior secondary II chemistry students’ in Eleme Local Government Area of Rivers State, Nigeria were randomly selected from four schools in the area of study. The specific purposes are (1) find out whether there is a significant difference in the mean achievement scores of students taught physical chemistry using the target task approach and the expository method (2) find out whether any significant difference in the mean achievement scores of high, average and low ability students taught physical chemistry using the target task approach and (3) find out the interaction effect of teaching method and ability level on students’ mean achievement in physical chemistry is not statistically significant. The research design was quasi- experimental while three null hypotheses were tested using the Kuder - Richardson formula 21 ( K- R- 21) a reliability coefficient of PCAT was determined which yield a ratio of 0.64. Findings indicated that students taught physical chemistry using the target task approach (TTA) performed significantly better in the physical chemistry achievement test (PCAT) than those taught with expository method. However target task approach was found to be more effective than the expository method in fostering students’ achievement in chemistry.