Random walk computer simulations are reported for the electric field autocorrelation of photons transmitted through multiple-scattering slabs. The results are used as a benchmark for judging the accuracy of competing theories of diffusing-wave spectroscopy (DWS), and also for distinguishing between errors introduced from the approximation of diffusive photon transport and from the continuum approximation that the total square wave-vector transfer of a transmitted photon is proportional to its path length in the material. An important conclusion is that these errors partially cancel, giving accuracies on the order of a few percent for typical experimental situations. Detailed comparisons are made as a function of optical thickness, boundary reflectivity, as well as scattering anisotropy; guidelines are generated for optimizing the analysis of actual DWS data in terms of the dynamics of individual scattering sites.