We present a simple model for surface disordering and study its consequences on reflectance anisotropy spectroscopy (RAS). Large unit cells are taken as a basis to introduce disorder by means of displacing the atoms from their equilibrium positions. Different displacement schemes are employed and ensemble averages are calculated in order to study the influence on the optical response. For reasons of computing time the semiempirical tight binding approach with an ${\mathrm{sp}}^{3}{s}^{*}$ basis is used to calculate the microscopic dielectric response of the surface, through which RAS is obtained. The well studied clean GaAs(110)(1\ifmmode\times\else\texttimes\fi{}1) surface is used as an example. We find that the spectral RAS structures of GaAs(110)(1\ifmmode\times\else\texttimes\fi{}1) follow a well defined behavior as a function of disorder and that a rather small number of surface atoms are needed only at equilibrium positions to produce already the RAS signal specific for the fully ordered surface reconstruction. This is a consequence of nearest neighbor interactions dominating the polarizability response and explains the fast dynamic response of RAS as compared to the diffraction methods which are limited by their large coherence length (low energy and reflection high energy electron diffraction).