The present study was initiated to determine how academic achievement and retention in chemistry is enhanced using the two instructional methods among SSII students and ascertained the differential performance of male and female students in chemistry with a view of improving student performance in chemistry. The study adopted a non-equivalent pretest, posttest control quasi-experimental design. A total of one hundred and eighteen senior secondary school II students in intact classes were chosen from three schools in Gboko Local Government Area of Benue State using purposive random sampling. The ages of the students ranged between 16-17 years. Data were collected using a 30-item multiple choice Chemistry Achievement Test (CAT), in organic chemistry. Students were assigned to a treatment and a control group. Three hypotheses were generated and tested which were tested at 0.05 level of significance. The data obtained were analyzed using descriptive statistics, t-test, Spearman's correlation coefficient and analysis of variance (ANOVA). There was significant difference in students performance when discussion and lecture strategies were used to teach chemistry (F[subscript cal] = 4.65 > F[subscript crit] = 3.85 at P < 0.05). There was significant difference in the retention ability of students exposed to discussion and lecture method ( r[subscript cal] = 0.9786 > 0.2353 at P < 0.05). There was significant difference in the performance of male and female students in the two groups (t[subscript cal] = 3.621 > t[subscript crit] = 2.000 at P < 0.05). The overall results showed that discussion instructional strategy significantly improved students' performance in chemistry better than the lecture instructional strategy. The study concluded that discussion enhanced better achievement and productivity than the lecture method. It was recommended that discussion method should be use to teach organic chemistry in Nigerian Senior Secondary Schools.