I agree with the "you may run into trouble" but I doubt they'd deny entry for a minor LPR on the first absence of less than a year when their LPR parent maintained residence in the US and the child was attending school in their home country.
I would agree that if the child will continue to go to school abroad then they should obtain a re-entry permit every time they will be out for more than 6 months to avoid future problems.
@OP, you can't edit the original post any longer.
The LPR child will be fine. Do not worry. It's fine for your son to come back in May 2012.
The LPR child would only run into trouble if the CBP officer makes a preliminary determination that he abandoned his LPR status. With an LPR parent maintaining a US resident, it's a uphill battle for the CBP to make that determination.
Furthermore, children cannot make the legal decision as to where they will live. That decision belongs with the parents. Does your 13 years old have the legal right to determine his resident??? NO. It's the parents' decision.
Be careful with travel outside the US. You've done the right thing by coming here for advice.
Even if the CBP officer determines your son has abandoned his LPR status, he does not have the authority to revoke the green card. At the least an immigration judge has to make that determination. Why go through this when the minor child's parent send him temporarily out of the country?????
