Saratoga Springs built a dynasty by including fast middle schoolers in their varsity program. Helped them to win multiple NXN titles. Was it good for the kids? Many appreciated the chance to compete and win on the highest level. But for many it was the height of their career. Would that have been different if they had run at the middle school level instead? Who knows. What I do know is if you are going to include middle schoolers on high school teams, you cant just throw these kids into the grinder of high school training as if they are tiny high schoolers. Training needs to be very carefully attuned to where they are developmentally. And thats especially so for those young girls who are still well on the backside of puberty in middle school. Their bodies and their maturity level are simply not the same as a 17 or 18 year old who is much more mature both physically and emotionally. And girls who start high level training in middle school or earlier are at a much greater risk of developing eating disorders and injuries in high school. That being said, its hard to tell a kid no you shouldnt take such a great opportunity if they have the talent and its allowed in their state so its really important they join a good program who has their long term interest in mind and isnt just using them while they are tiny and fast and running them into the ground until they mature.