The current study aimed to examine the associations between teacher presence and social scaffolding and preschool children's peer interactions. Using a time sampling method, peer interactions of 22 four- and five-year-old preschoolers (12 girls; M[subscript age] = 52.95 months) and teacher behavior were observed on two different days during various classroom activities in seven public preschool classrooms. Eco-behavioral analyses revealed that (a) teacher presence was negatively associated with positive peer interactions; (b) teacher absence was positively associated with negative peer interactions; (c) positive change of peer interactions was more likely to occur when the teacher was present; (d) children showed more positive peer interactions during child-directed activities than during adult-directed activities or daily routines and transitions; and (e) teacher's social scaffolding was positively associated with children's positive peer interactions although it occurred only for 3.61% of the intervals during which the teacher was in close proximity to children. In addition, although the likelihood for children's positive interaction was over 2 times higher in child-directed activities in comparison to adult-directed activities, teacher presence still seems very important for inhibiting negative peer interactions.