The credit for other dependents begins to phase out when the taxpayer's income is more than $200,000. This phaseout begins for married couples filing a joint tax return at $400,000.
You are allowed to forgo claiming your dependent so that he can claim the non refundable portion of the AOTC. That saves him all his tax (about $315) on the federal return. But it uses up one the 4 allowable AOTC. If there's no chance of collecting a bigger AOTC in the future, that shouldn't be a problem. He could/should claim the Lifetime Learning Credit (LLC) instead. The LLC only takes about $1600 of qualified expenses to get the same $315 credit.
