Teachers of inclusive early childhood education (ECE) are responsible for monitoring children's social skills achievement, and promoting social play between children with and without special educational needs (SEN). The Teacher Impression Scale (TIS) is an observational assessment developed for this purpose. This study aims to explore the social validity of the Swedish version of TIS, TIS-S, and to evaluate its effectiveness in identifying participants for peer-mediated interventions in Swedish preschools; by also testing the internal consistency, and the construct and criterion-related validity of the scale. The teachers (N = 16) observed children with SEN (n = 16) and without SEN (n = 16) in social play situations with TIS-S and subsequently answered a survey. Data were analysed quantitatively and qualitatively. Results demonstrate that the TIS-S has high internal reliability. The TIS-S also discriminated between the groups of children with and without SEN, which provided evidence of construct and criterion validity. Social validity was verified as the teachers reported that TIS-S was suitable for recognising individual children's need for support in interactions with peers, planning for adaptations for all children in the social learning environment, and reflecting on the complexity of children's social behaviour in play.