Introduction: No-one chooses the family one is born into. This truism lays the motivation for studies on the importance of family background for socioeconomic outcomes. Neither does anyone choose one’s birth order. Yet birth order has featured less in stratification research. Furthermore, whether it affects socioeconomic success, intelligence, and personality has been actively debated. Several scholars maintain that the effects are strong and robust (Zajonc, 1976; Zajonc, Markus and Markus, 1979; Black, Deveraux and Salvanes, 2005; 2007; Bjerkedal et al., 2007; Sulloway, 2007; Zajonc and Sulloway, 2007; Booth and Kee, 2009; Kristensen and Bjerkedal, 2010). Others have claimed that they are a ―methodological illusion‖ (Rodgers et al., 2000) based on unrepresentative samples and insufficient controls for confounding factors (also, Hauser and Sewell, 1985; Retherford and Sewell, 1991; Rodgers, 2001; Steelman et al., 2002). This study contributes to this ongoing discussion by using sibling data to analyze birth order effects on educational attainment in West Germany. The first objective is to simply estimate whether birth order matters in West Germany. Estimation of the effects of birth order is challenging because it correlates with family size, birth cohort, parental age, and other measured and unmeasured factors that can effect educational attainment (Blake, 1989; Hauser and Sewell, 1985; Black, Deveraux and Salvanes, 2005; 2007). I use sibling fixed-effects models—which control for all factors shared by the siblings—with controls for demographic factors, which differentiate siblings for estimates free from major confounding factors, and show the consequences for not addressing them.