This study suggests effectiveness of G-Learning (teaching and learning methodology utilizing interactions derived from game play) English afterschool class, which had been implemented for 3 months to 496 elementary school students in 5th grade at 31 elementary schools spread in the whole regions of Gyeonggi province. To achieve the goals of this study, two hypotheses were set in this study: 1) after conducting G-Learning English class, students' achievement in English study will increase, and 2) after conducting G-Learning English class, students' interest and confidence to English study will increase. Pre and post proficiency tests were conducted to verify the effectiveness of the G-Learning English class. A survey was also carried out with the participants of the class. The results showed that the students' achievement in reading was increased from 24.7 to 36.4 and vocabulary increased from 21.1 to 33.5 with statistical significance. The increase of the test score in three proficiency groups was as follow: high group was 9 points, middle group was 25 points, and low group was 38 points. Moreover, as for the affective factors toward English study, students' interest improved from 3.28 to 3.54 and confidence improved from 3.17 and all the aforementioned results showed statistical significance.