A check box field stores the values you select in the order that you select them separated by returns. If you click Teacher, staff, prospect and in that order, the filed stores:
Where a radio button format stores individual values unless you hold down the shift key and then it functions like a checkbox formatted field.
But note that the order in which you click the values changes the way the data is stored in the field.
What method are you using to filter the records? Is this a filtered portal? or are you using some other method?