The number of children diagnosed with Autism Spectrum Disorder (ASD) has skyrocketed over the past decade, with current estimates at one in 68 children diagnosed with the disorder (CDC, 2014). These increasing numbers, coupled with the push towards inclusion of children with disabilities in schools, have led to a greater number of children with ASD in regular education classrooms (US Department of Education, 2012). To better understand the social outcomes of these children, this study examined several factors believed to be associated with these outcomes. Student-teacher relationship quality as well as teacher attitudes and behaviors were examined for their effect on the social functioning of children with ASD in regular education classrooms. Participants included 22 parents and teachers of children with ASD from Kindergarten to third grade (18 male) who were placed in mainstream classrooms for at least 75% of the school day. Teachers and parents rated the child's level of social functioning and teachers rated the quality of their relationship with the child as well as their attitudes towards inclusion of students with disabilities in general. Classroom observations were conducted to examine direct teaching behaviors with regard to the teacher's emotional support, classroom management, and instructional support. Playground observations of the child were conducted to determine the child's level of social functioning during unstructured play periods. Overall child social functioning on the playground was related to STR conflict, and to some extent closeness, echoing previous findings from the typical and autism literature (Hamre & Pianta, 2001; Robertson, Chamberlain, & Kasari, 2003). Additionally there was evidence that naturalistic teacher behaviors may be related to child social skills as seen in the typically developing literature (Wilson, Pianta, & Stuhlman, 2007). While teacher attitudes towards inclusion were not related to child social functioning, they were related to child behavior problems (Avramidis & Norwich, 2002). Future researchers should look to examine how changes in STR and classroom climate influence the social functioning of children with ASD. Additionally, these results point to the potential for the development of social skills interventions by enhancing certain naturally occurring teacher behaviors in the classroom.