I disagree with your accountant. For a qualifying child the question is not how much he earned, it's how much he actually spent on his own support. If he put $27,000 in the bank or invested it, that is not money that he spent on support. And the value of the housing and meals that you provided is support that you paid for.
You can use the tool at the following link on the IRS web site to determine whether you can claim your son as a dependent.
Whom May I Claim as a Dependent?
