addClass and removeClass not working for me - not rocket science but I'm stuck

addClass and removeClass not working for me - not rocket science but I'm stuck

Hi all.
I am trying to do something that should be a no brainer, and I just can't get it right.  I have 3 buttons on my app.  When I click one, it shows the content for that button and the other div that was showing vanishes.  That works fine.  What DOESN'T work fine is the button doesn't get the class of active_button applied to it.  (The inactive buttons are  class=inactive_button).  So clicking a button to see that content should RemoveClass(active_button) from the active button and addClass to that button that is showing that content.  It isn't doing it.

Here's my jsfiddle link
http://jsfiddle.net/catlovergeek/Ldrs5ehb/

I hope someone can point out what must be a stupid little error!