ZhaoHong Han, my Second Language Acquisition professor at Teachers College, was the first teacher I ever had that showed data to support her students' progress over the course semester.  It made a lasting impression on me, and since then, I've tried to do the same with my students.

At the beginning of the term in my Reading 100 class, I give pre-tests for both reading and vocabulary.  During the last week of the semester, students take the same test again.  Then, after the results are scored, I give them the results of the whole class and show the students' individual progress (anonymously, of course).  This is pretty easy to set-up in an excel spreadsheet to make a simple graph to display.  Students are always so pleased to see evidence of their learning.  I make a big deal of it and make sure to acknowledge their hard work.  I also emphasize how the small score increases are actually quite significant. (And they are--the test is quite difficult).