Dr. Maya wanted to investigate whether attending preschool influenced how cooperatively preschool-aged children played with others. She used a self-selected sampling technique to recruit children for her observation by posting an advertisement on a local community social media group.

Dr. Maya wanted to observe how often children engaged in cooperative play (such as building blocks together). She videoed a group of children who did not attend preschool playing in their own homes (Condition A). Dr. Maya also visited a local preschool and videoed a different group of children, whose parents had volunteered in response to the advert, playing in their classroom (Condition B). She tallied the number of cooperative play behaviors displayed by each child.