Simple shear element tests can be used to examine numerous geotechnical problems; however, the cylindrical sample (NGI-type) direct simple shear (DSS) devices have been criticized for an inability to apply uniform stresses and strains, as well as the inability to fully define the stress state of the soil during shearing. Discrete element method (DEM) simulations offer researchers a means to explore the fundamental mechanisms driving the overall behavior of granular soil in simple shear, as well as improve understanding of the DSS device itself. Here three-dimensional DEM simulations of laminar NGI-type direct simple shear element tests and equivalent physical tests are compared to validate the numerical model. This study examines the sensitivity of the DEM simulation results to sample size, contact model and stiffness inputs, and ring wall boundary effects. Sample inhomogeneities are also considered by examining radial and vertical void ratio distributions throughout the sample. Both the physical experiments and the DEM simulations presented indicate that the observed material response is highly sensitive to the particle size relative to the sample dimensions. The results show that samples with a small number of relatively large particles are very sensitive to small changes in packing, and thus an exact match with the DEM simulation data cannot be expected. While increasing the number of particles greatly improved the agreement of the volumetric and stress-strain responses, the dense DEM samples are still initially much stiffer than the experimental results. This is most likely due to the fact that the inter-particle friction was artificially lowered during sample preparation for the DEM simulations to increase the sample density.