This paper describes the development and testing of a reaction control system (RCS) for a model rocket named FALCO-4. The rocket uses cold gas jets to keep itself perfectly vertical at low speeds. We first describe the mechanical layout of FALCO-4 and the characteristics of the cold gas propulsion system. We then propose a dynamical model of the rocket and a control scheme based on decoupled PID regulators for roll, pitch and yaw. The control scheme is then evaluated based on MATLAB simulation and flight data collected over 4 test flights that showed the RCS to work well even though vertical orientation was only partially achieved due to insufficient thrust from the cold gas thrusters. Finally, the present approach is evaluated and improvements are suggested.