Purpose: Hypertension (HTN) is associated with increased cardiovascular risk and unhealthy lifestyles in adults. However, data on both physiological and lifestyle factors associated with abnormal blood pressure (BP) in adolescents, as well as the effectiveness of interventions in improving these factors among adolescents with abnormal BP, is scarce. Methods: Students enrolled in a middle-school-based wellness program, Project Healthy Schools (PHS), between 2005–2016 were eligible. Three systolic (SBP) and diastolic (DBP) BP measurements were taken pre-PHS and post-PHS; averages of the final two were analyzed. Students were grouped by baseline BP: abnormal BP (≥90th percentile for SBP and/or DBP, or ≥120/80 mmHg) or normal BP (<90th percentile for SBP and/or DBP, or <120/80 mmHg). Demographics, physiologic measures, and health behaviors were compared between groups pre- and post-PHS. Results: Of 2,865 students, 812 (28.3%) had abnormal BP. Median SBP was 119 mmHg in abnormal BP students and 103 mmHg in normal BP students (p < .001). Females were less likely to have abnormal BP than males (48.4% vs. 51.6%, p < .01). Pre-PHS, abnormal BP students were more likely to be overweight (62.3% vs. 28.2%, p < .001) or obese (38.9% vs. 11.3%, p < .001) than normal BP students. Their total cholesterol, triglycerides, random glucose, resting, and recovery heart rates were also higher, and they had worse dietary and sedentary habits. Post-PHS, abnormal BP students demonstrated greater reduction in SBP (−4.0 vs. 2.8 mmHg, p < .001) and DBP (–3.3 vs. 8 mmHg, p < .001) than normal BP students. Conclusions: Abnormal BP was prevalent and associated with worse cardiometabolic health parameters and behaviors at baseline. Abnormal BP students demonstrated significant improvements in BP post-PHS, suggesting school-based programs may be effective as nonpharmacological lifestyle interventions in this population.