One thing people often overlook in SAT/ACT testing is that they are very LONG tests. If a child does not have good stamina or has ADD, it may be very difficult for them physically and mentally, even if they are in the right intellectual ballpark to do well. My son, for instance, found the process exhausting at age 11, and for that reason, I am not planning to have my younger children take these until they are about 11.
OTOH, if a child has endurance and is ready earlier, I see no reason not to let them dive in!
