This last year I implemented the super improver wall with great success. As students showed improvement, they received a star next to their name on the super improver wall. Here is a picture and more information about the wall: http://luria-learning.blogspot.com/2012/02/super-improvers-wall.html
Some activities were automatic stars. For example, my weakest readers knew that they could get a star for beating their scores in super speed 1000 and that they would have a chance to practice with me or a volunteer a few times a week. We would work till they earned a star. This was incredibly motivating.
Students could also earn stars for improving their test scores on their weekly math and vocabulary tests. I would have to say that this did not motivate students quite like the super speed 1000, and I now understand why.
An interesting article on the timing of rewards from edweek.com shows that students actually do better when the reward is linked very closely in time to the action. Actually, if you give the reward first, and then have the student earn the reward, students will work even harder. They don't want to "loose" the reward that you have already given them.
With super speed 1000, I was able to put their name on the board to show that they were going to earn a reward immediately. While it might not have been posted on their chart till later, they still received the immediate gratification of seeing their name go up.
With the vocabulary and math tests, it took me longer to see if they had improved, graded them, and then eventually put up their stars. Sometimes I might not put them up for 2-5 days. And because I gave the tests on Fridays, the weekend would add a few more days to the wait.
I'm not sure what the solution to this would be. I was almost wondering if I could put on the board - Your star this week - with the student's name and their score that would have them earn a star. Then, if they didn't make it I would erase the star. What do you think?