And if your e-file is rejected because of the father e-filing ahead of you....claim the son as a dependent anyhow...and print-mail it in.
Once the IRS sees the conflict, they will send both of you letters asking you to support yoru claim. The IRS doesn't know who the son actually lived with all year when there are competing claims. Keep as many documents backing up yoru claim as possible. School records and address of record, medical exam documents/bills showing address..etc.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
