Whether the UTMA is considered his money or not, depends on if he's reached 'Legal age', which is dependent on your state law where the UTMA was established, typically age 18 or 21 (in the state of Florida for property it's age 25 - so it really can depend). The investment firm that holds the account/helped you create it; should be able to provide you with this information, as it will affect how you file taxes. 

If he's not of legal age, then the assets are still part of the custodian's taxable estate, until he takes possession at legal age. Also, you have the option to claim him and take and take his educational tax credits (form 1098). 

This may be more advantageous for you, because when he's filing alone, he'll take the standard deduction of $6,300 and the personal exemption of $4,050. Based on his income, some of these deductions won't even be utilized and that's before considering tuition credits. In this situation, he could still file to claim his earned income (which cannot go on your return), if he would like to for a refund (he would be below the filing requirements, not including his investment income). 

However, if he is of legal age and the UTMA is considered his, then you won't qualify to claim him, for numerous reasons, and he must file on his own. This information should also be in your paperwork for when you formed the account. Let me know if you have any questions.