A long-standing controversy in the literature over the role of spin exchange in spur kinetics has been investigated for a four-radical spur using a modified Monte Carlo simulation technique which explicitly incorporates the quantum mechanics of the system. The dimensionality of the spin Hamiltonian is reduced using permutation group theory to improve the efficiency of the simulation program, Comparison of an exponential model of the exchange interaction with well-known approximations under a variety of conditions indicates that the "contact exchange" (CE) approximation of Brocklehurst and Highashimura is accurate to within 10% in most circumstances.