Hello and thanks you for using Just Answer. U.S. citizens who maintain a tax home outside the U.S. and its territories are still subject to tax on worldwide income and must file a tax return.
Your son will be able to exclude up to $91,500 (for 2010) of his foreign earned income from his taxable income. He must file Forms 1040 and 2555 to receive the credit. The forms are available at the IRS web site, www.irs.gov,.