In this study we investigated the perceptions of male and female college students (N = 208) who evaluated preschoolers actual aggressive and prosocial behavior, which was obtained from naturalistic observations and presented as detailed transcripts. Findings revealed that men were not as accurate as women were in identifying relational aggression and prosocial behavior. Coders were generally similar in their identification of physical and verbal aggression. This study suggests that gender biases and stereotypes exist in the evaluation of relational aggression and prosocial behavior, which included assessments of relational inclusion. Researchers must take precautionary steps to investigate and ameliorate the gender biases of potential informants, which, if not addressed, may lead to errors in a myriad of standard methodological instruments (e.g., observations, teacher reports, and survey designs) currently used by psychologists and relationship scholars.