“…Nevertheless, despite a long history of research on HW, the strength of the relationship between HW and academic achievement is not yet clear (e.g. Cooper, 1989;Dettmers, Trautwein, & Ludtke, 2009;Farrow, Tymms, & Henderson, 1999;Paschal, Weinstein, & Walberg, 1984;Ronning, 2011;Trautwein & Köller, 2003;Trautwein, Köller, Schmitz, & Baumert, 2002). The explanation could be due to the variety of used research designs (Cooper et al, 2006), or different data analysis strategies (Trautwein, Schnyder, Niggli, Neuman, & Lüdtke, 2009) which do not allow data comparison.…”