Rubber-modified cementitious substances and various methods of making such substances or components thereof. One embodiment of the substance includes a mix of cement and composite particles, wherein essentially each of the composite particles has a rubber core enclosed in an inorganic exterior and wherein the rubber core is chemically coupled to the inorganic exterior. The chemical coupling between the rubber core and the inorganic exterior and the bonding between the inorganic exterior and the cement result in a rubber-modified cementitious substance that has greater strength than comparable conventional rubber-modified cementitious substances. One embodiment of the method of making a rubber-modified cementitious substance includes (1) reacting a coupling agent with rubber particles and inorganic particles to yield composite particles, wherein essentially each of the composite particles has a rubber core enclosed in an inorganic exterior and (2) combining the composite particles with a cementitious substance to yield a rubber-modified cementitious substance.