Visual acuity (VA) screening is highly valid in school-aged children for detecting visual impairments. This study aims to provide a comprehensive profile of VA among school-aged children (6-17 years old) from Lisbon, Portugal. Specifically, it focuses on estimating the prevalence of abnormal VA (VA < 0.8 in the worst eye) and establishing age-specific normative reference values (percentiles) for monocular and binocular VA within this urban sample. We performed an observational, descriptive, and cross-sectional study that included healthy children aged 6 to 17 years. Convenience sampling was used in three educational centers in Lisbon. Retinoscopy and monocular VA (right eye, left eye, and the eye with the lowest) and binocular VA were assessed using the Herman Snellen optotype. Descriptive statistics, prevalence of abnormal VA (worst-eye VA < 0.8), and monocular and binocular VA percentiles were calculated for the whole cohort and by age. The sample consisted of 2215 children (49.6% of males; and 9.4 ± 2.6 years old). Binocular VA, right-eye VA, left-eye VA, and VA worst eye in the study cohort showed ranges of 0.92-1.00, 0.90-0.95, 0.89-0.97, and 0.85-0.94, respectively, for ages 6-17 years. In total, 86.8% of the study population had a normal VA (≥0.8). VA deficit was mild (0.8 < AV ≥ 0.3), moderate (0.3 < AV ≥ 0.125), and severe (VA < 0.125) in 10.5%, 1.1%, and 1.6% of children, respectively. Our study provides both age-specific normative reference values for visual acuity in Portuguese children and prevalence estimates for visual acuity deficits. These findings offer critical data to support early detection strategies and the development of age-adjusted vision-screening protocols in school-aged populations.