This study applies a "within-family, age-snapshot design" to investigate differences between siblings in the development of compliance during the preschool years by disaggregating situational, within-family, and between-family effects. The aim of the study was to investigate the relation between sibling differences in compliance and the within-family factors birth order and differential parenting, as well as interactions between these factors. Using observational data of 311 Dutch families (self-identified as culturally Dutch) with 2 children when each child was 3 and 4 years old (firstborns: 36.2 months old; SD = 3.6; 48% girls, second-borns (2 years later): 36.67 months old; SD = 0.62; 47% girls) and both parents. Three-level cross-classified multilevel models showed main effects of observed sibling noncompliance and differential verbal discipline on noncompliance. In addition, second-born children were more compliant than their firstborn siblings, but only when the firstborn was disciplined physically more often than his/her younger sibling. The results provide evidence that birth-order effects may partially be explained by differential parenting and suggest that differences between siblings cannot be fully understood without taking into account the influence of both direct and indirect sibling effects.