What your son (or anybody else) puts on their W-4 at work has no bearing on the tax return itself apart from how much withholding there is to pay the tax. Withholding is the amount your request your employer to withhold on your W-4.
On line 5, you tell how many allowances you with to claim. If you choose zero, they will withhold the most based on the tables (see Pub 15 link below). The more allowances, the smaller the refund, BUT, you will get a little more in each paycheck. In that way, you can choose if you prefer to have more money in your paycheck or at the end of the year in your refund.
If your son incorrectly claimed himself as independent, he would have to amend his return and state that he is being claimed as a dependent and pay back any refund he was not entitled to. You may then mail in your return claiming him and his education credit. Since he has already filed and his social security number has be "used", you can't efile.
What your son (or anybody else) puts on their W-4 at work has no bearing on the tax return itself apart from how much withholding there is to pay the tax. Withholding is the amount your request your employer to withhold on your W-4.
On line 5, you tell how many allowances you with to claim. If you choose zero, they will withhold the most based on the tables (see Pub 15 link below). The more allowances, the smaller the refund, BUT, you will get a little more in each paycheck. In that way, you can choose if you prefer to have more money in your paycheck or at the end of the year in your refund.
If your son incorrectly claimed himself as independent, he would have to amend his return and state that he is being claimed as a dependent and pay back any refund he was not entitled to. You may then mail in your return claiming him and his education credit. Since he has already filed and his social security number has be "used", you can't efile.