Get down on all four with your weight evenly distributed between your elbows and knees. Make sure your knees are directly under your hip joints and your elbows are directly under your shoulder sockets. Engage your core muscles by pulling your belly button into your spine.
Extend one of your legs back; your toes should be pointed and barely touching the ground. Keeping your leg perfectly straight, and your hips level and stationary, lift your leg as high as you can without arching your back. Slowly lower your leg to within an inch of the ground but do not touch until you are done with all repetitions.
Switch to other leg and repeat.
The kneeling rear leg raise is a great exercise for the butt muscles. This will tone as well as shape and lift the glutes. To get the most out of it be sure to squeeze your butt as tight as you can at the top of the motion. To make it harder, add an ankle weight and do the leg raising motion slower.