2. If talking to the person doesn't work, talk to your manager about how your work is being affected.
3. In both cases stick to specific behaviours and how they impact your work and the team's output. It's not your place to evaluate other people's overall job performance.
It’s very unlikely that you’ll be able to help this other person “improve” (and it might cause new problems for you if you try).
You might also need to realize that the other person isn’t underperforming and that you don’t have full information about the situation.
Then stop helping, completely. And let nature take it's course, or help if necessary. It's nature's way.
:-)
Are they uncomfortable in a group setting, going through health issues?
Let’s define underperforming fairly. Are they new? Just because they don’t match the team, maybe they’re learning still. It’s good to reflect.
Also, talk to them, be a friend. It’s a team not a competition.
But probably your college is not an underperformer.