Uncertainty in the performance of high-temperature structural materials remains a challenge to their development and implementation in extreme environments. Materials in these applications are often exposed to high heat-fluxes resulting in very high temperatures, steep temperature gradients, oxidation, and erosion. Ultra-high temperature ceramics (UHTCs; e.g., refractory carbides and borides) are being considered for these applications due to their high temperature capability and high thermal conductivity. However, UHTCs are prone to oxidation under flight conditions and have low fracture toughness, which increases the risk of using them in demanding structural applications. This presentation will focus on our work in addressing these challenges via fiber reinforcement, and improving our understanding of oxidation behavior via an oxidation kinetics model and validating the model under relevant service conditions. The goal is to develop comprehensive modeling tools that overcome facility-dependent conditions and biases for improved the prediction of performance and life.