Could someone let me know what the advantages and any disadvantages of participating in this kind of testing are? My child is 10.
Honestly, I don't see any disadvantages. Three of my four kids have done it and enjoyed it (the fourth never wanted to, even though she's now extremely successful in college and did very well on standardized testing in HS - but we always left it up to them). We didn't prepare in any way, but they never felt they were in way over their heads, and were okay with not knowing everything.
For us, it was most beneficial when it came to OTHER people - teachers, administrators, even family (explaining why a child who loved math and was very far ahead might want to learn something besides what was taught at school, or justifying why it was a good idea to send a child to the middle school for math). It's a great, objective way "explain" your child to other people.
