The relationship between salivary cortisol levels at the beginning of the school year and parent reports of temperament using the Children's Behavior Questionnaire (CBQ) were investigated in 35 first graders. Cortisol was sampled in the morning, afternoon, and evening on the first and fifth days of school and two weekend days later in the school year. On the first day of school compared to weekend days, children displayed a steeper cortisol slope across the day due to lower afternoon and evening levels. By the fifth day of school, cortisol levels, on average, were not different than on weekend days. However, using change scores to reflect the response to school days relative to weekend days, children who scored higher in Surgency (i.e., enjoyment of intense play, high activity level, impulsivity, lack of shyness) continued to display a steeper cortisol slope on the fifth day of school with higher morning and lower evening cortisol levels. In contrast, shyness, which negatively contributes to Surgency, was positively correlated with evening change scores on the fifth day of school.