As to which test, a post above describes the differences.
As to prep, it really depends on your goal. For my son, we did literally no prep. The goal was simply to see where he would score and if he would make the CTY cutoff for the summer programs He was already in the GT program at his school (although that ended at middle school). I believe the programs are designed to identify kids that score well without prep, but of course that doesn’t mean that all the test takers go in cold.
As I mentioned above, both tests serve the same purpose but only the SAT can be used for SET qualification. So, lacking any other reason to differentiate, I recommend the SAT.
I had my D do one of the sample SATs from CB a few weeks before the test just so she was familiar with the mechanics, forms, types of questions, etc. No content/skill preparation or studying.
Years ago my son did one test in 7th and the other in 8th grade. So happy to hear parents are only having the child get familiar with the test. It is a great time to take the test cold- when results won’t be known for college admissions. Even in HS these kids can get the top scores without any extra prep. Some do so earlier- remember that Bell curve, some kids will fall in the extreme right portion, better than most others considered gifted. Our kids are who they are, it is nice to see where they fit among the top percentile(s).
My son took the SAT cold and qualified for the program. He was also playing water polo and was in Boy Scouts. We saw the cost of the programs and I looked at the content. Maybe if they were cheaper we would have had him go. But he went to scout camp for a week. He played in a summer water polo league which, with several practices a week and weekend games, made for a busy summer.
He was already in the gifted program at school and I thought the summer break from academics was actually good for him.
SET is through JHU. You can read more about it here:
https://cty.jhu.edu/set/eligibility/index.html
It doesn’t look like the cogito.org site is still functioning, but lookin through these resources as well, might give insight to opportunities in general: https://cty.jhu.edu/resources/academic-opportunities/
If you think your child has the potential to score very highly, I’d recommend the SAT, which, as others have noted, also allows for JHU SET qualification.
Like many others, son didn’t study for test, but did take one practice exam from the CB site to familiarize himself with format.
For my son, qualifying for SET had four advantages:
The ACT and SAT are a lot more similar than they used to be. I would just pick whichever test is used by your state. One advantage of starting with the SAT is that it’s prep for the PSAT test, which could get you national merit scholarship money or discounts, even free rides at some universities.
Our son already attended a gifted school but had some test anxiety. He took the ACT. He was a little nervous, but did fairly well (25) in 7th grade with no prep. There will be some questions (geometry, primarily) that your child may not have been exposed to yet, so don’t expect a high school level score at that age.
When he had to take the test for real in HS, he scored a 33 (10th grade) and then 36 (11th grade) with minimal (a few hours) studying. He had no anxiety because he already experienced the test. It also helped on the PSAT, and he qualified for NM too.