The Niger Delta region of Nigeria faces persistent water quality challenges driven by rapid urbanization, oil-related industrial activity, and aging infrastructure. Despite numerous environmental assessments in the region, drinking water quality within schools—where children represent a highly vulnerable population—remains largely unexplored. This study provides a targeted evaluation of metal(loid) contamination in tap water from 30 primary and secondary schools distributed across urban (Port Harcourt, Warri) and peri-urban/rural communities. Concentrations of Pb, Cd, As, Hg, Cr, Ni, Cu, Zn, Fe, and Mn were determined using atomic absorption spectrometry, with rigorous QA/QC procedures. Samples were collected under flushed conditions and acidified, representing total recoverable metal fractions. Mean concentrations (µg/L) decreased in the order Zn > Fe > Cu > Mn > Pb > Ni > Cr > As > Cd > Hg. Lead exceeded the WHO guideline (10 µg/L) in 47% of schools. Entropy-Weighted Water Quality Index (EWQI) results classified 80% of samples as excellent to good, whereas 20% were medium to poor. Multivariate analyses (PCA with KMO = 0.72; Bartlett’s p < 0.001) identified two dominant factors: (1) infrastructure-related corrosion (Pb–Zn–Cu–Fe) and (2) geogenic/industrial influences (As–Hg–Cr). Health risk assessment following USEPA guidelines indicated that non-carcinogenic risk was generally below the safety threshold (HI < 1), although exceedances occurred in 10% of schools for children. Carcinogenic risk values for Pb and As surpassed the acceptable limit (1 × 10⁻⁴) in 30% of locations. Although limited by sample size and single-season sampling, the findings highlight infrastructure deterioration as a key determinant of school drinking water quality and underscore the need for systematic monitoring and targeted remediation to protect children’s health.