Adding tuition is lowering my refund

Hi.  My son is a full time student and when I just put his eligible tuition into Turbotax, it actually decreased his refund by half.  He made more than the basic personal amount at his part time job.  Why would he have to pay more tax as a student?  Is it mandatory to submit his eligible tuition and declare he is a student?  It seems he would be better off not saying he is a student but I don't know if that is a mandatory declaration.  Thanks for any help!