What is the meaning Of the cartoon in the Montgomery Advertiser that Scout doesn't understand?

This cartoon shows up in Chapter 12.  It shows Atticus as a little boy wearing shorts and no shoes.  He's chained to a desk and doing school work while some girls call to him.

The meaning of the cartoon is that Atticus is sort of a geek.  He is always working and is too serious.  As Jem says, it shows that Atticus does things that wouldn't get done otherwise, but the cartoon is making fun of Atticus for doing them.  The cartoon shows this because it has him chained to a desk working while the other kids are trying to get him to do something else.