We introduce coherent inelastic neutron scattering with isotope substitution as a technique for measuring site-specific information on the vibrational dynamics of amorphous solids. The technique is used to extract experimentally the partial vibrational density of states G α (E) for both Ge and Se in the prototypical networkforming glass GeSe 2 , where α specifies the chemical species and E denotes the energy. The efficacy of the approximations used in interpreting the experimental data is validated by using a first-principles model, for which the set of true partial vibrational density of states is directly accessible. Our approach offers an opportunity for exploring accurately the vibrational dynamics of disordered materials.