Many researchers believe that start of schooling is a crucial period for children, their cognitive and social development.  Class or school composition have a significant effect on progress and achievement in elementary school (e.g. McLean et al., 2016). Some authors focused on the effect of non-academic composition characteristics such as average socio-economic status or proportion of immigrants within class (school) (Van der Slik, Driessen & De Bot, 2006; Perry & McConney, 2010). Other examined the effect of averaged class or school achievements or class academic homogeneity on individual performance and progress (Hanushek et al., 2003; Hoffer, 1992).

It has been shown that averaged class or school achievements have the positive effect on learning progress or individual achievements (e.g.  Zimmer & Toma, 2000). This effect has been confirmed  in elementary school (McLean et al., 2016 ), in  secondary and high school as well (Carman & Zhang,2012; De Fraine et al., 2003;  Ding & Lehrer, 2007).

Findings about the effect of classroom homogeneity on academic progress are inconsistent. There are some evidences that students’ progress in academically homogeneous classes may be higher than in heterogeneous classes (Ding, Lehrer, 2007). At the same time, other authors do not confirm significance of this effect (e.g. Kiss, 2013; Hanushek et al., 2003). The effect of class homogeneity is predominantly estimated in secondary school (Kaur, 2016; Lavy, Silva,& Weinhardt, 2012). There are fewer studies focused on estimation this effect in elementary school (e.g. Burns & Mason, 2002).

It has been also demonstrated that effect of class composition on academic progress varies for students with different abilities. There is evidence that peers achievements and homogeneity of class have the effect on progress of students with high ability only (Hoffer, 1992; Ding, Lehler, 2007).

The overarching goal of our study is to estimate the effect of class average achievements and homogeneity  on academic progress during the first year of schooling. We attempt both to identify effect of class composition on academic progress and ascertain whether this effect is generalizable across different groups of students and subjects.

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