The flight instructor reported that before demonstrating spin recovery to the student pilot, he confirmed that the weight and balance met the requirements for the utility category. The flight instructor stated that as the spin reached the fully developed state, he began to execute the recovery procedure by reducing power to idle, ailerons remained at neutral, opposite rudder control to stop the turn, and the elevator forward. During the recovery, he noted that the airspeed did not exceed 110 mph which was 12 mph below the design maneuvering speed of 122 mph. Subsequently, the windshield shattered during the recovery process. The flight instructor immediately landed the airplane at the airport that he was maneuvering over without further incident. An examination of the airplane revealed that about half of the windshield separated. The airplane fuselage, wings and empennage were not damaged. The reason for the windshield failure was not determined.