<p>This study assessed indoor air quality by measuring size-segregated Particulate Matter (PM₁₀, PM_2.5, PM₁), and gaseous pollutants (CO, SO₂, NO_2, and CO₂) concentration in different schools of Dhanbad city and characterize their indoor dust by using FESEM-EDX, FTIR, and XRD analysis. Fine particles (PM_2.5) surpass the Indian criteria at half of the sites and the WHO limits at all sites. Amongst all schools, Dhaiya Middle School (DMS) shows the highest values of size-segregated PM₁₀, PM_2.5, and PM₁ (131.49 ± 34.73, 82.46 ± 15.49, and 54.71 ± 8.52&#xa0;µg/m³ for summer and 139.78 ± 36.87, 94.86 ± 17.75, and 58.45 ± 10.68&#xa0;µg/m³ for winter). Dayanand Anglo Vedic Public School (DAV) shows a minimum value due to closed and controlled microenvironments, more vegetation outside, and properly designed classrooms. Indoor dust characterization demonstrated that particles in classroom dust came in various morphologies, including spherical, flaky, angular, irregular, and porous shapes. Smaller particles are present with clay aluminosilicates, which are mostly made up of irregularly shaped soil particles. Ca was found in far greater concentrations than the other crustal elements, most likely due to the chalk (mostly CaCO₃) used in blackboards. Higher PM ratios in the DMS indicate preferential indoor infiltration of finer particles through openings such as doors and windows, whereas indoor PM₁₀ is mostly determined by resuspension caused by student movement, air circulation, and other classroom activities. Functional groups such as hydroxyl (-OH), aliphatic carbon (-CH₂), carbonyl (-CO), and amino (-NH₂) have been observed in classroom dust by FTIR analysis, originating from diverse sources including construction activities, motor vehicle exhaust, and biogenic processes. Schools had significant concentrations of minerals, including quartz, vaterite, and calcite, according to X-ray diffraction (XRD).</p>