Abstract: This study aimed at identifying the impact of Reinforcement in academic achievement among fourth primary grade students in the Kingdom of Bahrain. The study used a quasi-experimental method following the pre- post test design for both the experimental and the control groups. the sample consisted of (30) students from Aljasra Primary School for Boys in Bahrain were randomly assigned to experimental groups and the control group by 15 students in each group. The study used the oral achievement test, written achievement test and table of Reinforcements. The results showed the effectiveness of reinforcement in academic achievement development of fourth grade students in the Kingdom of Bahrain, where the results showed a statistically significant differences between the mean scores of the experimental group and the mean scores of members of the control group on the achievement test, and the differences in favor of the experimental group. Key words: Reinforcement, achievement, primary school.