Position yourself to get a clear view of the stage where the school concert will take place. Sit in the front row, or stand to the side of the room, against the walls, so you're not blocking anyone's view. Use a tripod to steady the camera for sharper pictures.
Stand on the side of the stage if the school staff will allow it. Use a wide angle lens to photograph the entire width of the stage from a side view. Use a telephoto lens to zoom in on one person and for other close up detail pictures. Take a variety of pictures.
Use a flash on the SLR camera, if the lights are dimmed across the entire stage and you are more than seven feet away from the person you are photographing. If a spotlight is used on the one person you want to photograph, a flash is not needed.
Set the camera. If manual adjustments are comfortable for you, set the exposure bracketing to overexpose by one or two stops if the lights are dimmed. Adjust your aperture to the largest opening possible, and keep the shutter speed between 1/60 to 1/125. Set the camera on the Auto or Program mode if you aren't familiar with manual settings and adjustments.
Take a variety of photos. Shoot a wide angle view of the entire scene, close-up photos of your child and medium-range shots of groups of children together. Take pictures of the teachers introducing the students and the students getting hugs afterwards. Ask another parent to take a picture of your family with the child who performed in the school concert.