@MyrtleD , I believe your son will be a strong candidate for Swarthmore. I wouldn’t agree that a rejection from Swarthmore necessarily means a rejection from other similarly selective LACs. Their applicant pools are highly self selecting which means that it’s difficult to predict why candidates with similar profiles experience different outcomes.
How many reaches really depends on the strength and reliability of your son’s matches and safeties. If he’s comfortable with your in-state public or his other less selectives, then he can expand the top end. An ED/EA rejection or deferral can allows time to recalibrate in the RD round, adding more matches and safeties.
I would suggest that your son consider Williams. Not only does Williams excel in math, sciences and overall academics, but it also has an excellent music program with multiple performance opportunities for non-majors.
https://music.williams.edu/category/ensembles/
Williams doesn’t have minors, but double majoring is common and encouraged. No matter what his intended major he should submit a music supplement. I believe your son’s involvement in music would be a substantial boost in admissions at Williams, possibly moreso than at other LACs of similar selectivity.
I noticed the discussion on your other thread about foreign languages. I believe that most LACs will be flexible on their foreign language requirements for admission, but their FL degree requirements vary widely. If he’s not interested in studying a FL at the college level then he should look carefully at each college’s degree requirements and competency criteria and make sure he will be able to “place out.”
https://www.swarthmore.edu/modern-languages-literatures/language-requirement
http://collegecatalog.uchicago.edu/thecollege/thecurriculum/#othercollegerequirements
I think Wesleyan would be a good fit for him as well.