A method for making impact resistant molding compositions wherein a hard phase having a glass transition temperature above 25.degree. C. and consisting principally of methyl methacrylate is polymerized at least partially in a first stage, following which the monomers of a rubbery phase whose polymers have a glass transition temperature below 25.degree. C. are added in a second stage and the polymerization is carried to completion, polymerization of the hard phase in the first stage being performed in a presence of an oil soluble free radical initiator and of an organosulfur chain transfer agent having at least two thiol groups in the molecule, and polymerization of the monomers of the rubbery phase in the second stage being carried out with graft crosslinkers in the presence of the previously formed hard phase.