In addition to the requirements that VolvoGirl stated, you must have provided more than half of the person's total support for the year. Tuition alone might not be more than half of the person's total support. Support includes housing, food, clothing, transportation, and all other living expenses.
The $4,000 income limit is for 2015. If you are working on your 2014 taxes, the income limit is $3,950.
