I see people advacating racing if your not ready. I disagree because someone can get discouraged with the result and that can set them back, some athletes don't have a problem, but others do. It's true you need an idea of correct paces, but you get that though a solid training block. If your running, for example 6x800 in 2:30, with a 400 meter recovery, you have an idea of your fitness. Towards the end of the training block, you should run a few time trials. Some people are head cases and if you through them in a race and their not far enough along in their workouts and run way off what they wanted, it can screw with them. Let them run a few time trials before, but you have an idea of your fitness after a solid training block. You just don't want to screw with some athletes heads.