It's hard to tell from the scan but the date is actually 1906, I can't get a good close up scan of the date. Also, it's hard to believe that these are high school players, a couple could possibly pass for high school but I could be wrong.
Here are a couple pics of Sline from a 1907 Reach Guide and 1907 Spalding Guide, kind of looks close.
sline2.JPG