There's always something interesting bound to happen when two of your students are siblings..

My students Kane and Anne are a classic example.

Kane : Teacher, what do you and my sister do in your class?
Me : free talk
Kane : Everyday?
Me : Yes. Why
Kane : She can use my book, it's ok with me.
Me : She would rather not.
Kane : But she can, she's aleady good in English! I used to be better than her but because she went abroad for a while she's now better than me.
Me : It's not about who's better than who Kane. She's preparing for a speech contest.
Kane : But that's not fair. I study the book everyday.
Me : Why do you hate your book so much?
Kane : *grumbles* She will also study the book if you tell her to.
Me : We can make Friday our games day, Kane. You like that?
Kane : *beams* or we can play games everyday, teacher.
Me : Give it up, Kane. Get your book.
Kane : teacher do you think Anne is better than me?
Me : No, I don't think so. I think you're both very impressive.
Kane : You're not telling the truth.
Me : *getting fed up* That's the truth. Now get your book, Kane.
Kane : *big sighs*
Me : (haaaaaaayyy.. kids!!!)

Me : Hey Anne, what do you think about Kane's book?
Anne : No teacher. I don't want to study that book. My brother is very bad.
Me : He's very bad?
Anne : Yes, he talked to you last night about my class.
Me : Excuse me?
Anne : I was listening on the other line. *said with utmost smugness*
Me : Oh, you call that eavesdropping, Anne. Not very good.
Anne : Yes, teacher I know. I'm sorry, but I know my brother. He's really mean.
           Teacher, is my brother talkative in your class?
Me : Hmmm, why don't you ask him?
Anne : I don't think so.
Me : Yeah? Why not?
Anne : Because he never talks to me, not even in Korean. But me, I'm very, very talkative.
Me : *smiles* Yeah, I noticed.