Int. J. Environ. Res. Public Health 2010, 7 3461 and keep subtracting by four until they were told to stop at the three-minute mark. The acute noise stressor was a challenge that involved listening via headphones to a three-minute recorded mix of loud street noises, office machinery, and people speaking, with intermittent random noise bursts (80 dBA peaks) [25]. 3. Results 3.1. Identification of Covariates Preliminary analyses were conducted to identify covariates. Relative to children in the quiet school, children in the noisy school had a significantly higher BMI (20.66 vs. 30.97 mean BMI) (t187 = 11.05, p = 0.000) and were trending toward being older (9.21 vs. 9.67 mean years old) (t187 =1.87, p = 0.06). In addition, the experimenters reported slightly more problems due to noise and/or interruptions in the testing environment of the noisy school (mean = 1.22) than the quiet school (mean = 0.71) (t187 = 3.61, p = 0.000). We also identified sex of the child as a covariate because BMI was significantly higher in girls (mean = 27.44) than boys (mean = 24.26) (t187 = 2.69, p = 0.008) and DBP reactivity during the math challenge was trending toward being higher in girls (mean = 6.58 mm HG change) than boys (mean = 3.20 mm HG change) (t187 = 1.72, p = 0.09). Thus, sex, age, BMI and level of testing problems were used as covariates in subsequent analyses. 3.2. Resting Blood Pressure Resting SBP and DBP outcomes were analyzed using separate ANCOVAs. School (noisy vs. quiet) was the independent variable and sex, age, BMI, and testing problems were covariates. As shown in Table 1, on average children in the noisy school tended to have lower blood pressure than children in the quiet school; but the differences were statistically non-significant. Table 1. Resting systolic and diastolic blood pressure among children in the quiet versus noisy elementary school (n = 189). Quiet School Noisy School Blood Pressure M SE M SD Fdf Systolic 1 94.63 2.00 92.22 2.01 0.561,183 Diastolic 1 61.71 1.60 56.81 1.62 3.651,183 1 Means adjusted for sex, age, BMI, and testing problems. p 0.452 0.058 3.3. Blood Pressure Reactivity during Acute Noise and Non-Noise Stressor Exposure SBP and DBP reactivity outcomes were analyzed using separate ANCOVAs with school (noisy vs. quite) as the between-subjects factor and type of acute stressor (noise vs. math challenge) as the within-subjects factor. Each ANCOVA statistically adjusted for the corresponding baseline value of resting blood pressure (e.g., resting SBP was covaried in analyses of SBP reactivity), in addition to sex, age, BMI, and testing problems. There was no effect of order of presentation of challenge, so analyses collapsed across order. Analyses of SBP reactivity revealed a significant main effect of school (F1,182 = 8.73, p = 0.004), no significant main effect of type of acute stressor (F1,182 = 2.77, p = 0.098),