Lightweight Engineered Cementitious Composites (LWECCs) offer superior mechanical properties, making them promising construction materials for lightweight concrete structures. However, available research primarily focuses on small-scale testing, with limited data on their structural performance. Contributing to this knowledge gap, the present study investigates the shear behavior of reinforced beams cast with six different engineered cementitious composites that were developed with densities ranging from 1740 to 2080 kg/m³, using various filler materials. Specifically, silica sand (SS) as a normal weight filler was used to produce two normal weight engineered cementitious composites (NWECCs), while other four LWECCs were produced using expanded slate aggregate (SL) alone or combined with either crumb rubber (CR) or powder rubber (PR). Two types of fibers, polyvinyl alcohol (PVA) and polypropylene (PP), were incorporated into both the LWECCs and NWECs. Additionally, a beam cast with conventional lightweight concrete (LWC) at a density of approximately 1850 kg/m3 was tested for comparison. The performance of all beams was evaluated in terms of cracking behavior, load-deflection response, ultimate shear capacity, normalized shear capacity, post-diagonal cracking resistance, deformability, and energy absorption capacity. The shear capacity of all tested beams was also compared to that estimated by available existing design models. Results showed that NWECC and LWECC beams with PVA fibers performed better than those with PP fibers. SL was effective in developing LWECC with comparable density and strength to LWC, but with higher ultimate shear capacity, normalized shear strength, post-diagonal cracking resistance, deformability index, and energy absorption capacity by 57.8%, 64%, 45.9%, 112.1%, and 112.5%, respectively. Further reductions in beam self-weights, down to 1740 kg/m³, were achieved by incorporating either CR or PR alongside SL, and these beams continued to outperform the LWC beam. Combining SL with PR resulted in a lighter, higher-performing LWECC beam compared to that developed with SL and CR, due to PR's lower specific gravity and finer particles, which contributed to improved mechanical properties, indicating a potentially denser microstructure. The design model, particularly tailored for beams reinforced with polymeric fibers, exhibited the most accurate predictions when compared to the experimental data obtained in the study.