Updated clinical practice guidelines for screening blood pressures in pediatric patients were published in 2017. They differ from the previous guideline, known as the Fourth Report, providing updated population normal values and blood pressure categorization. We hypothesized that the prevalence of abnormal blood pressure in children and adolescents would be higher using the new clinical practice guidelines. We present a cross‐sectional study of screening blood pressure values for children 3 to 18 years of age obtained during well‐child visits at a primary care clinic. All blood pressure values were categorized using both the Fourth Report and the Clinical Practice Guideline. A total of 2635 blood pressure measurements were extracted, and 2600 were eligible for analysis. Using the clinical practice guideline, the prevalence of hypertension increased to 17.85% compared to 9.5% per the Fourth Report (P < 0.0001). Of those patients classified as having a normal blood pressure by the Fourth Report, 12% changed to abnormal when applying the Clinical Practice Guideline. All subgroups had a significant increase in the prevalence of abnormal blood pressure. The most dramatic increase in the prevalence of stage 1 and stage 2 hypertension was seen in six patient subgroups: males, 3‐12 years of age, Hispanic ethnicity, race designated as other, normal weight, and overweight. Applying the new Clinical Practice Guideline increased the prevalence of elevated blood pressure and stage 1 and stage 2 hypertension in children and adolescents, requiring more follow‐up and intervention than previously expected for this patient population.