As the construction industry moves toward precast structures, a more mechanically robust concrete is required. To provide joints with higher mechanical toughness, we propose reinforcing the mortar with a polymeric lattice. This study considers the mechanical effects of reinforcing concrete with a polymeric lattice and compares this new technique against the standard fiber-reinforced method. We investigate the octet lattice, which is notable for its high specific strength. Lattices with 23.4 mm unit cells were prototyped out of polylactic acid using a thermoplastic extrusion-based 3D printer. These lattices were placed in a rectangular mold, infiltrated with concrete, and vibrated. The resulting specimens were tested for flexural strength in four-point bending on a hydraulic testing machine. Bending test results show that the lattice-reinforced beams achieve a net deflection at peak load that is 2.5 times greater than that of the fiber-reinforced beams. Further, the lattice-reinforced beams obtain toughness and peak load values comparable to the fiber-reinforced beams while allowing for easier processing. Fabrication of these lattice structures for use in construction can readily be scaled, as the polymeric lattices can be manufactured through injection molding.