Typically, the reduction of the load and strain data obtained during an Iosipescu shear test assumes constant shear strain and shear stress distributions. While this is nominally correct and simplifies the data reduction, it provides no insight into the shear stress-shear strain distribution and can lead to theoretically inconsistent experimental results. In this study, an Idaho Iosipescu test fixture, two sizes of strain gages, an assumed power law for the strain distribution, and the Richard-Blacklock stress-strain relationship have been combined to model both the shear strain and the shear stress profile across the gage section. The results show a strain distribution dependent on both load and laminate layup and the difference between the shear stress and the shear strain profile. The initial shear moduli found from the nonlinear model show an insignificant difference between the two layups which is in agreement with composite theory.