Research on educational mobility is concerned with inequalities between families. Differences in innate abilities and parental responses lead, however, to educational differences between siblings. If parental responses vary by family socioeconomic background, within-family inequality can affect between-family inequality (i.e., educational mobility). This study uses data from the German Socio-Economic Panel Study (SOEP) to test whether sibling similarity in education varies by family socioeconomic background. In addition, I test whether the effects of birth order, birth spacing, and maternal age on education vary by family background. Results show that sibling similarity in education is similar in low– and high–socioeconomic status families. The negative influences of a higher birth order and a younger maternal age on educational attainment, however, are concentrated in socioeconomically disadvantaged families. These findings suggest that socioeconomically advantaged families do not generally compensate for ability differences between their children but that they compensate for disadvantageous life events.