My son is amending his return so we can claim him. what if they process our return before his amended return?

If you have already sent in your return without him as a dependent, you can always do an amendment to correct for this and, it would be best to wait until you receive your refund to do an amendment on your return to prevent delays.  Remember, you have three years to amend a return so you can wait for your refund before doing the corrections.

If  you have not yet sent off your return, it would be best to wait for his amendment to be processed.  If his amendment is not completed by the end of March I would suggest you contact the IRS customer service line at 1 800 829 1040, for updates so you can process yours before the deadline.

It does not matter. The IRS will process your return without coordinating with his return. It he never gets around to amending, 9-12 months later you will both hear from the IRS.

You do not need to wait until his amended return is fully processed, or even submitted, to claim him on your return. But, you cannot e-file. You will have to mail in a paper return.