A microanalysis of social interaction in a preschool classroom revealed ways in which children and teachers "co-constructed" the rudiments of school culture during the first three days of school. Findings are based on videotapes, teachers' notes, and daily field notes taken by a group of observers. The three domains of the establishment of school culture identified involved ways to establish: (1) the use of materials and space; (2) procedures, formats, and motifs; and (3) roles and relationships. A total of 1,570 microevents, called School Culture Actions and Messages (SCAMs), were coded into a matrix of the 3 domains and 16 inductive categories. Categories were arranged on a continuum that began with teachers' relatively proactive and independent contributions, moved through responsive SCAMs which were yoked to social context, and then moved to shared control between teachers and children. From this midpoint, the continuum moved through responsive child SCAMs to independent control by children. Discussion characterizes the children as seekers of meaning and the teachers as their guides. Teachers and children have proactive and responsive positions in a complex "co-construction process." The early days when children and teachers are intensely involved in learning to live together is contrasted with a later time when children's social focus turns to their peers. The appendix provides a definition of SCAMs and an outline describing teacher, shared, and child SCAMs. (RH)