This study aims to investigate the flexural behavior of simply supported one-way reinforced concrete (RC) slabs constructed with high-strength concrete (HSC) and normal-strength concrete (NSC), reinforced with either glass fiber reinforced polymer (GFRP) bars or conventional steel reinforcement. Four large-scale reinforced concrete (RC) slabs were tested under four-point bending. The failure and cracking loads, deflection, crack patterns, and failure modes were considered as main parameters. Results showed that GFRP-reinforced slabs (both NSC and HSC) had higher deflections by 2.60 times and lower ultimate loads by 21.0% to 32.0% compared to steel-reinforced slabs. GFRP-reinforced specimens also experienced sudden failure due to bar rupture and exhibited wider cracks. The experimental results compared with those from analytical predictions based on ACI 440, CAN/CSA S806, and Eurocode 2, the results were in accordance. While CSA S806-12 slightly underestimated cracking loads for HSC-GFRP slabs, it provided accurate mid-span deflection estimates. Eurocode 2 predictions for crack widths were within 10% of the values observed.