The angle-dependent resonant Rayleigh scattering of light from excitons in a disordered quantum well is studied theoretically. An enhancement of the scattered intensity peaked on the backscattering direction is predicted, for values of the parameters corresponding to realistic GaAs/AlGaAs heterostructures. It is shown that this effect can be isolated by measuring the differential enhancement between two different scattering directions. An analysis in terms of perturbation theory provides a simple analytical approximation of the measurable quantity.