Using laxatives and throwing up to manage weight?

I do believe that using laxatives and throwing up to manage weight is damaging. I don't know how damaging it is for your son and how damaging it could be in the future. The biggest problem with this is you have no way of knowing if this will turn into a life long eating disorder or not. It is possible that he does what he needs to do for school sports, then goes back to "normal" afterwards with minimal damage. It is also possible that he uses his new skills for weight management and coping in the future.

It scares me that coaches push for weight loss (good reason for the sport) but don't also talk about the down side and how this is only for this short period of time. There are consequences for using too many laxatives and there are consequences for excessive throwing up. You, as the parent, will need to weight the pros and cons so you can feel good about this decision. I see how difficult this situation is for you. You want to support and encourage your son but don't want an eating disorder on your hands. 

I think it's important that you feel good about how you proceed so you don't have regrets in the future. You can only make the best decision on this situation based on the information you have today. You can do research on consequences of eating disorders so you have the information and way the facts with what you know is true about your son. You can also have him see a counselor to discuss how he feels about food and his body to get a professional opinion (who has more information from your son).

I wish you the best of luck with this. I wish there was an easy answer for you.