Anyone will come to your party. Real ones come over to help you study for the test you’re failing.

A party asks nothing of anybody. There is food and company and a reason to turn up, so attendance there measures almost nothing about the people in the room. An evening spent on a subject that is not theirs, in your house, with you in a bad mood, has no reward attached at all. That is where the sorting happens.

Be honest with one person about a class you are losing and ask them to come over for an hour. Notice who says yes. And when somebody else is in that position, offer before they have to ask, because asking is the hard part.