The main findings can be summarized as follows. First, the estimated critical age at immigration is about 10. Thus, children arriving in the country up to about the 4 th grade seem to be catching up well with their peers either born in Sweden or immigrating before the start of preschool. This result is stable for both boys and girls and for children of different origin. Second, any similar marked critical age at immigration is not found using cross-sectional estimation, and above the age of 10 the sibling-difference estimates are 27-54 percent less negative than the cross-sectional ones. This is an expected pattern if the cross-sectional estimates are inflated by selection bias due to parents’ migration decisions. Third, as with natives, immigrant girls outperform immigrant boys (immigrant girls arriving in Sweden up to about the 4 th grade also perform on a level above that of native boys). The negative effects due to short duration of residence are significantly larger for girls than for boys, although the slopes of the age-at-immigration-performance profiles are similar. Fourth, there are striking differences between immigrants from different source areas. Children of Western, East European and Asian origins outperform other immigrant children. The steepest average age-at-immigration-performance-profiles, on the other hand, can be observed for children of African, Middle Eastern and Asian origins. Fifth, few years in a Swedish school prior to graduation is significantly less negative for the performance in mathematics than it is in terms of GPA which demonstrates the importance of Sweden-specific skills.

Not sure if I understand it correctly, here is my understanding of this summary.

1+2: An important factor is at which age did the immigrant child arrive to Sweden. If they arrived younger than 10 years (4th grade), they will be okay at school. If older than 10 years, they will have problems.

3: Girls outperform boys; this effect is for both native and immigrant children.

4: Not all immigrants are the same. Children of Western, East European and Asian origins perfom better, children of African, Middle Eastern and Asian origins perform worse. (Seems to me they mentioned Asian children twice here.)

5: In mathematics the disadvantage of the immigrants is smaller, so it seems the performance problems are with Sweden-specific topics.