A new floating wall consolidometer-type bender element testing system was developed to study the stiffness anisotropy of clays at applied vertical stresses up to 800 kPa. One-dimensional slurry-consolidated Georgia RP-2 kaolinite samples, prepared with 0.005 and 1 mol/l NaCl solutions, were tested in this system. A floating wall design eliminated the detrimental bending moment that acts upon the horizontally installed benders as a result of soil settlement in a traditional fixed wall setup, which significantly improved the signal quality and bender reuse. Floating wall–soil interface resistance was quantified with pulling tests. Analytical equations were then derived to calculate the wall resistance-corrected vertical effective stress. As a result, stresses applied to the soil were more accurately determined. The bender element (BE) test was used to measure kaolinite's shear wave velocity (Vs), thereby quantifying the small strain stiffness of soils. Average Vs results for RP-2 kaolinite were lower than those for other kaolinites reported in the literature. This was postulated to be primarily due to the longer and more tortuous chains of particle contacts associated with the smaller median diameter (d50 = 0.36 μm) of RP-2 kaolinite samples. BE test results indicated that Vs increased with stress, density, and concentration. The hierarchy of Vs in three orthogonal directions (i.e., hh > hv > vh) agreed with results in the literature. It was also illustrated that Vs anisotropy increased with applied stress and decreased during unloading. In addition, a comparison was made between the BE test in the new floating wall consolidometer and the BE test in a triaxial testing setup.