It's not really for "underprivilaged" kids only. I had a big brother when i was younger (til i was about 15 or 16 i guess) and i had him since i was 9.5 years old. My mom only signed me up because my parents were divorced and my dad never saw me. We're no longer officially big/little brothers but we're really good friends.
He has two kids (was childless when we were paired up) but his wife died of cancer last year, so I've been supporting and helping him as much as I can. We'll be lifelong friends for sure. He is one of the most interesting, make that the most interesting, people I've ever met.
I'm almost 20 now btw, so wow...been 10 years. hard to believe.
I commend anyone who does this. Anyone who does is a saint because it really does make a difference. I'll be doing the same when I'm older.