37 lbs of Garbage

So while we were out walking a mile around the school, I noticed the kindergartners picking up trash on the school grounds.  We waved to them, they waved back, we continued our walk, and they continued to collect garbage and put it in the large trash bags their teachers had brought outside. I ran into one of their teachers at the end of the day.
  "Great job!  It looks a lot better out there," I told her.
  "We collected 37 pounds of trash!" she told me excitedly.

They used the scale in the nurse's office.  But first they had the kids estimate how much it would all weigh!  Not only that, they found out who had the closest estimate and how far off they were.  And to top it all off, they put the bags in order from heaviest to lightest.