“…In nearly all American studies, students' cognitive developments were moderated by parent's socio-economic status and their educational level. Depending on these moderating variables, children's knowledge and skills deteriorated or improved over the course of the summer vacation (e.g., Allinder et al, 1992;Cooper et al, 1996;Cooper, Valentine, Chariton, & Melson, 2003;Alexander et al, 2001Alexander et al, , 2007Alexander et al, , 2012. In contrast, the few European studies that exist found limited evidence for moderating variables.…”