This study aimed at detemining the effect of using the formative remedial strategy in teaching history on the instant and delayed achievemnet of 10th grade students in the Islamic Sciences Institutes. The study sample was made of 60 students of 10th garde at Muscat Institute for Islamic Sciences. The sample was divided randomly into two groups: the experimental group (30) students who were taught by using formative strategy and a controlled group (30) students who were taught by the traditonal teaching method. All students in both groups were given an achievment test at the end of the experiment which lasted for 8 weeks. The same test was implemented again on all students after 3 weeks of the experiment's application to check the achievement result in Histroy teaching. Results were analysed by using 'T-test' for two independent groups to check the remedy over the variables (instant and delayed) achievement in order to measure the performance of both groups (experimental and controlled) in the final achievment test. The results showed significant differences at the level of (0.05) between the average of both groups (experimental and controlled) in the final achievment test (instant and delayed) in favour of the experimental group. Due to these results, the reseacher recommends the using of formative remedial strategy in the teaching process because of its advantageous impact in raising students' achievement.