Int. J. Environ. Res. Public Health 2010, 7 2.2. Participants 3460 A total of 189 boys and girls from 3rd and 6th grade classrooms participated in this study: 95 from the quiet school and 94 from the noisy school. Sex of child was distributed fairly evenly between the noisy school (51.6% males) and quiet school (52.1% males). Class level also was distributed fairly evenly between the noisy school (52.5% third graders) and quiet school (55.3% third graders). 2.3. Experimental Design The study used a non-equivalent, two-group (quiet vs. noisy school) repeated-measures (noise challenge reactivity vs. math challenge reactivity) research design. We used a counterbalanced design to control for order effects, with children randomly assigned to order of presentation of the acute stressors. 2.4. Measures Resting and reactive blood pressure. Blood pressure was measured using a non-invasive ambulatory blood pressure monitoring device manufactured by Finapress Medical Systems (Amsterdam, The Netherlands). The device was applied to the middle finger of the child’s non-dominant hand. Three readings were taken at 1-minute intervals. The first reading allowed the child to adapt to the device. The average of the last two readings was used to create the resting SBP and resting DBP scores. Blood pressure also was measured three times at one-minute intervals during the acute stressors, a noise challenge and a math challenge, which are described below. The reactivity scores were calculated by subtracting the average resting blood pressure reading from the average of the three blood pressure readings taken during each challenge (e.g., math challenge reactivity on SBP = mean math challenge SBP—resting SBP). Body Mass Index (BMI). BMI was measured using the standard metric formula: weight in kilograms/height in meters squared (km/m2). Rating of testing environment. At the end of each study session with a child, experimenters recorded their overall impressions of the testing environment using a 4-point scale: 0 = no problems, quiet, no interruptions; 1 = minor problems, occasional background noise and/or an interruption; 2 = moderate problems, low background noise throughout testing and/or two interruptions; 3 = major problems, high levels of background noise throughout testing period and/or more than two interruptions. 2.5. Procedures The study procedures were reviewed and approved by the appropriate institutional review boards and informed consent was obtained from participating study schools. Each child was assessed individually under standardized conditions at the schools. The child sat at a desk across from the experimenter. The child’s height (meters) and weight (kilograms) were measured, a brief survey was completed to collect demographic data (e.g., age), resting blood pressure was assessed, and reactive blood pressure was assessed while the child was exposed to a noise challenge and a non-noise challenge. There was a three-minute resting period between the challenges. The acute non-noise stressor was a math challenge that required participants to subtract aloud by four from a large number