Being a full-time student has no actual direct bearing on your taxable income or your refund. It can affect the amount of your standard deduction when you are eligible to be claimed as a dependent of another taxpayer (as the vast majority of 19-year-old full-time students will be), but it doesn't affect your refund.
Your refund is a function of the total (and type) of income and the amount of tax that is withheld.
It sounds like you aren't quite finished with your return if you are still being asked questions about deductions. You need to answer those, just the same as a full-time employed taxpayer would. It could result in additional funds being added to your refund.
If you aren't receiving the majority of your federal withholding back, then you made enough income to owe some federal tax. If you are looking at your social security and medicare taxes and considering those in your calculations, those are never considered as part of refund calculation.
There are several items listed on his W-2 that he will not get back. These are things like social security tax withheld, medicare tax withheld, and local income tax. In some counties there are ways to get the local taxes back if he doesn't live in that county and files to get it back from the local government. That's something I know nothing about.
He would only get refunds, depending on his income from the federal tax paid from the federal 1040 and the state tax back from his state tax form. You didn't mention if he had a summer job, internship, or things of that nature. If he had substantial interest from bank accounts, certificates of deposits, dividends from stocks, those can certainly count as income and prevent him from getting the refund he expected.
In addition, if any income was from self-employment, he also has to pay social security and medicare tax on that income.
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