This is important! If you do this, you should rollover the money to an IRA first.
Assuming this is a pre-tax 401k, withdrawals are always subject to regular income tax. If you are under age 59-1/2, withdrawals are also subject to a 10% penalty, unless you separated from the company at age 55 or higher. There is no exception for higher education expenses.
However, if you withdraw money from an IRA, you can claim an exemption to the additional 10% penalty if you use the money to pay qualified higher education expenses for yourself, your spouse, a child, or grandchild. That means that, to avoid the additional 10% penalty, you should do a rollover from the 401k to an IRA (this is non-taxable), then withdraw from the IRA (this will be subject to regular income tax but not a 10% penalty.)
