The Jakarta Mega Urban Region (MUR) has expanded to become one of the largest mega-urban regions in the world. In this paper, we revisit Castle's seminal study on the education and ethnic composition of Jakarta using the 1961 Population Census. Using data from the full count 2010 Population Census, we examine the spatial patterns in the educational gradients of the population across the Jakarta MUR, and how such patterns may be explained by internal migration and the ethnic composition at the sub-district (kecamatan) level. We found that population movement from the core to the outer areas has softened the historically extremely sharp gradation in educational attainment across the MUR. We show the dominance of the Sundanese and Bantenese ethnic groups in rural hinterlands of the MUR where the average educational attainment is relatively low, and note this question of rurality versus ethnicity when interpreting our results.