Yes Rocky Mountain Academic Talent Search (RMATS) also does EXPLORE for grades 3-6. RMATS, Duke TIP, and Northwestern (along with JHU & ? Maybe C-mites?)are all part of the national talent search and you may sign up with any one of them and pay their fee. We live in RMATS "region" and have previously participated in the Duke TIP and JHU CTY. You do NOT need to sign up for more than one in the same year (unless you're going for the awards in your home region). I like getting mailings from all of them but no longer sign up for more than one per kid.
