My youngest son was having problems focusing on his math homework. It's true - there are more fun things in life than math. He's at the age where he doesn't want (or need) the help, but he needs a nudge sometimes.
After a few minutes I walked up to him and said "how many problems do you have left?"
"Do you think you can have them done in 10 minutes?"
I placed 6 pennies on the table. "Every time you get a problem done take one of these pennies. But at the end of 10 minutes I'm going to come back and take whatever pennies are left."
Three minutes later the homework was done.
Sometimes a little change of focus is all it takes.