Only Children and Siblings: The Differences in Educational Attainment and Family Background Marta Hirschová PhD student Institute of Sociological Studies, Faculty of Social Sciences, Charles University in Prague martahirschova@email.cz Abstract: This paper investigates the effect of number of siblings on educational attainment in the Czech Republic in 2005. The negative effect is considered documented in western countries. However, it has also been shown that in some subpopulations this relationship either does not exist or is even positive (Downey, Neubauer 1998; Maralani 2006). Guo and Van Wey formed a suspicion that educational outcomes can be influenced by some unobserved and unmeasured characteristic which influences both the level of education and number of siblings. If these factors are not included in the analysis, this leads to distortion when the number of siblings appear as an influential factor. This paper presents the part of the analysis which is carried out on the first wave of Generations and Gender Survey (2005). The research sample is limited to the subpopulation who was born between 1973-1987 and finished educational process. The results of binary logistic regression show that the effect of the number of siblings on educational attainment is minimal after control of individual, family and structural factors. The negative effect begins to be factually and statistically significant from three (or more) siblings. Only children and children with two siblings have approximately the same chance to reach higher educational level, however their family background is differnet. Only child has more often higher educated mother and lives in single or step parent family. In contrast, child with two siblings have most often lower educated mother and lives in more stable family structure. These findings can be indicative of non-linear effect. Keywords: siblings, only child, education, GGS