A system and method for selectively stimulating a plurality of producing zones of a wellbore in oil and gas wells, the system being cemented within the wellbore. The system includes a plurality of modules connected in a string wherein the modules can be selectively actuated to stimulate producing zones adjacent the modules. Each module includes a sleeve shiftable between a closed position and a treating position where a plurality of radial passageways are exposed to the central passageway of the assembly. The system includes a wiper plug that is adapted to pass through ball seats of various sizes in the plurality of modules and an acid solution pumped into the string to break down the cement at the producing zones. The system may include at least one natural rubber wiper ball to remove residual cement from the string.