re: Any one who works for an HR dept.

So you believe they have no intention of hiring you but are stringing you along until the end of the semester?

I usually go with the truth. I'd tell them that you need to ensure you are gainfully employed by X date or you will be forced to consider other options. Tell them that you've enjoyed your time there and want to continue, but it would be irresponsible for you to put your family in that situation because you've got bills to pay. Of course, you have to be willing to act if they tell you that they can't meet your deadline. If you're not willing to get back on your tools, then maybe you don't want to be so bold if you think it might jeopardize your situation.