This study investigated whether preschoolers would spontaneously say thank you in a familiar context without their parents' presence. Two hundred and fifty 3 1/2- to 4 1/2-year-olds played a game with their teachers and received a reward from either an unfamiliar peer or adult. Across conditions, 37 percent of the children said thank you spontaneously, more than in previous studies. The frequency of the spontaneous use of thank you was assessed as a function of sex, socioeconomic status, and listener status. Preschool-aged girls said thank you spontaneously more than boys, χ2(1) = 7.95, p < .01. Also, children from families of low economic status said thank you spontaneously more than children from middle income families, χ2(1) = 7.17, p < .01. This finding does not appear to be due to racial differences. Finally, the preschoolers said thank you spontaneously more to the adult than to the peer, χ2(1) = 4.27, p < .05. These results are discussed in terms of their implications for pragmatic socialization and the acquisition of politeness formulas such as thank you. (Routines, politeness formulas, pragmatic socialization, sex differences, socioeconomic differences, language and status)