One of my kids did it for a few years, and had a great time and an excellent experience. As a sixth grader, she built a remote control robot that had to perform different functions (and she did not have any particular engineering bent, she just ended up doing it). The judging can be kind of arbitrary, and it is heartbreaking if/when they lose after the amount of time they put into it. (The robot entry was beaten by a team that rode a tricycle to perform the same function...). Also, it is a very time consuming activityt to do well. But I think the experience overall was very positive and fun. A good teamwork experience, too.
