My sons return, if I mark someone else will claim him as a dependent he has Tax Refund. If I mark No one will claim him he has Tax Due. This seems opposite, why?

The standard deduction for a single person when no one else can claim them is $12,000 is $6,350 max.

 So, if he made $14,000 his taxable income when no one else could claim him would be $2,000 (14,000-12,000). 

If he made $14,000 and someone else is claiming him his taxable income would be $7,650 ($14,000-$6,350) 

Both amounts put him in the 10% tax bracket, so his tax liability when someone claims him would be $765 as opposed to $200 if no one claims him.

  If he only had $500 withheld from his pay he would be short $265 (765-500) when someone claims him but would have a refund of $300 (500-200) if no one claims him.