In this study, experimental results for the control of the seesaw system which is an under-actuated system by the state feedback method using linear quadratic regulator (LQR) are presented. The system consists of two arms that are fixed from the center of gravity and turn freely. Balance control is provided by a linear rail between the two arms and a cart that can move on the rail. Since the proposed system contains a nonlinear and unstable structure, it is used for the educational purposes in the analysis of nonlinear systems in the control systems courses and laboratories. The mathematical model of the system is given and the balance control on the real-time system has been successfully accomplished by the full state feedback method using Bryson's rule and linear quadratic regulator. The designed controller is implemented by a rapid control prototyping method on an ARM (Advanced RISC Machine) based development kit. External disturbances were applied to the system in order to test the performance of the controller and it was observed that it was able to control the system under disturbances.