It is a school picture of my grandmother's, Mildred Wagner, who married James Denton Osborn.  My grandmother is the tall girl in the back next to the teacher.  

 

My grandmother was born in Rock Port in 1904 and married by May of 1919.  I would guess that this photo was taken in 1916 at the very earliest.  That would make her 12, and she looks older than that to me in the photo.  She was married in 1919, so that would be the latest the photo would have been taken.  By comparing other photos I have of her, I am guessing she was 14 and the picture was taken around 1918.

The names of other students are written on the back, but not in a way that you can identify which name goes with which kid.  The cardboard surround is broken, so some of the information is broken off.  I have traced several of the names back to Atchison County census records.