Why is the standard deduction on my son's tax return NOT $6,300?

I claim my son as a dependent but I file a tax return for him because he had about $1,500 income and distribution from college funds.  TurboTax says his standard deduction is $1907.  This does not make sense.  I don't know where the number came from.  He has no itemized deduction so this is not a mistake in choosing the wrong deduction method.  How do I fix it?