You didn't tell us the boy's age ... nor any other facts about his status.
I would suggest that he not leave the US until AFTER he has a certificate of citizenship AND a US passport.
Plus, given the great schools that we have in the US .. you should discuss why he'd want to go to the Philippines for school.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.
More facts are necessary to determine whether your son qualifies for US citizenship.
Mr. Shusterman is a former INS Trial Attorney (1976-82) with over 35 years of immigration experience. His response to your question is general in nature, as not all the facts are known to him. You should retain an attorney experienced in immigration law to review all the facts in your case in order to receive advice specific to your case. Mr. Shusterman's statement above does not create an attorney/client relationship.
A USC can return to the USA whenever he or she wishes. USA is his or her home country.
The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter,not should it be viewed as establishing an attorney client relationship of any kind.