Hi Ania,
Some of top colleges do require all SAT scores or strongly encourage you to do so. As a result, having too many SAT scores in student's record may not be a good thing. Yale and Stanford requires all scores. Princeton strongly suggest that you send in all scores (whatever that means). Harvard and MIT are okay with score choice. The policy for Cal-Tech is unknown.
Another thing to consider is that the SAT scores are sent to high schools where they are put on official HS transcript (at least that is the case for my kids). So colleges will still see them even you use score choice.
I am not sure about the benefit of taking SAT before the student is fully ready especially the kid had already done so in middle school. If you just want your son to have more practice, you can buy a book.
Following is a URL to policy of individual colleges on score choice (compiled by college board).
http://professionals.collegeboard.com/profdownload/sat-score-use-practices-list.pdf
