If the AP course is more rigorous than the college course, why is the student taking the college course? Around here, CC courses are a joke, and the public schools won't give credit for them (except as remedial courses, in certain cases).
If the child is too young to take HS AP courses, but is interested in a subject, why not take a free online course (Coursera or similar)?
AP scores are good for five years, I think. If the child is younger than 8th grade, he probably needs to wait to take the AP exam so it would count for credit or placement for college. I would recommend taking the AP exam if the student is familiar with the material, as college credit or placement may be useful. Both of my older two were/are able to have two majors because they entered college with a lot of AP credit.
