Social capital created in disparate contexts like family and school are interrelated to facilitate academic achievement. However, the broadness of the concept of social capital has made empirical analyses difficult. Against this backdrop, this study tried to construct the concept with relational, structural, and cognitional dimensions and to clarify the features of each dimension in order to capture the diverse characteristics of social capital. Based on the construct, we investigated the change in the English grades of 2,058 students of from 62 middle schools during the period from between year 2010 to 2012. We used 3-level Hierarchical Linear Model with panel data from Seoul Education Longitudinal Study. The main findings are as follows. First, First structural and cognitional social capital from family does improve the level of academic achievement when school offers the same features of social capital. Also, relational social capital does help improving the level of achievement of low class students by moderating the influence of structural social capital. These findings do have significance in understanding the characteristics of social capital and the mechanism they work to positively influence the academic achievement of students.