Geopolymers are an inorganic polymeric material composed of alumina, silica, and alkali metal oxides. Monolithic geopolymer is brittle and susceptible to dehydration cracking at elevated temperatures. The addition of a reinforcing phase not only improves strength and toughness but also maintains the structural integrity of the material at elevated temperatures. For this study, potassium-based geopolymer (KGP) is reinforced with varying weight percent of chamotte particles. Chamotte is kaolinite grade clay calcined at 1350°C to produce 38% crystalline mullite, as well as metastable cristobalite and quartz. The chemical composition of the chamotte is almost identical to that of the metakaolin used to create the geopolymer, however, its crystalline nature prevents reactivity with the caustic potassium silicate solution and it remains as a particulate reinforcement. Flexural strength is evaluated at room temperature and in situ at elevated temperatures to just below the leucite crystallization temperature. Reinforcement with 25 wt% chamotte has shown a two-fold increase in room-temperature flexural strength. Flexural strength is also evaluated at room temperature after heating above the leucite crystallization temperature to determine if the chamotte aids in maintaining structural integrity during the volumetric contraction and destructive transformation from cubic to tetragonal symmetry upon forming leucite.