26 sibling dyads, aged 4 to 12 yrs, were surreptitiously observed on 2 occasions during free play in the home. Mothers were absent during baseline observations. During the experimental session mothers were present and either ignored sibling coercion (Ignore Condition) or verbally intervened (Reprimand Condition). Reprimands consisted of a "stop-it" statement plus rationale and redirection. Children in the reprimand condition displayed lower rates of coercion and higher probabilities of skillful verbal reasoning than children in the Ignore Condition. Aversive sibling reactions to coercion were unaffected by the experimental manipulation. Theoretical implications, methodological limitations, and suggestions for further research are discussed. (PsycINFO Database Record (c) 2017 APA, all rights reserved)