The sensitivity of three thermal-energy model problems to anisotropic scattering was investigated by comparing double P5 solutions with P3 and P1 scattering expansions. Results indicate that P3 scattering effects can be significant in the calculation of absorption rates in certain sensitive plane-geometry configurations. Monte Carlo calculations were also performed for one of these problems, using two different anisotropic scattering representations: the transport approximation; and a “histogram” kernel, which match the first two and four Legendre moments of the scattering kernel, respectively. The transport approximation was found to give discrepancies of eight to nine percent in thermal absorption rates, and it is concluded that this scattering representation can lead to serious errors in Monte Carlo calculations.