The purpose of the present study was to identify predictors of children's cortisol responses after the transition to kindergarten. Morning salivary cortisol was measured in 50 children 1 week before and 1 week after they began kindergarten. Children who experienced a greater degree of change between their preschool and kindergarten routines and who had infrequent preschool experiences exhibited the largest increases in morning cortisols after kindergarten entry. Children whose parents indicated that they would have an easier, rather than more difficult, time adapting to kindergarten also tended to be more reactive in their morning cortisol levels after kindergarten entry. Results provide new insight into experiential and individual-difference factors that predict children's physiological reactivity and self-regulation during times of transition and potential stress.

The link between socioeconomic status (SES) and health has been clearly established: individuals with low SES have poorer health than those individuals with high SES. 1,2 There is also evidence of a graded association at all levels of SES. 3 In the child development literature, very little is known about what factors in children's lives may contribute to the SES-health association. One domain that may be important is a child's peer relationships. Is a child's position in the peer group hierarchy analogous to an adult's position in the socioeconomic status hierarchy? If so, would hierarchy position in preschool be related to health? In addition, perhaps individual differences in children's cardiovascular reactions to stress mediate the association between SES and health. These two factors, social dominance and cardiovascular reactivity, can be measured in very young children with valid research methods. The objective of this cross-sectional study was to examine relations among SES, social dominance, cardiovascular reactivity, and physical and mental health outcomes in preschool children.Seventy 3-5-year-olds (62% boys; 47% Caucasian, 10% African American, 15% Asian, and 28% multiethnic) and their parents participated. Families came primarily from the middle and upper class with 9% reporting a family income of less than $20,000, 6% between $20,000 and $40,000, 23% between $40,000 and $60,000, 26% between $60,000 and $80,000, 13% between $80,000 and $100,000, and 23% over $100,000. Children completed a 30-minute physiologic protocol composed of developmentally challenging tasks during which their heart rate and blood pressure were monitored. 4,5 To assess social dominance, children were observed in naturally occurring peer interactions at the preschools. 6,7 Parents completed questionnaires assessing family demographics and their children's physical and mental health and behavior. For this paper, family income was used as the SES indicator. A six-item