My circle tracker is a spreadsheet that I make for each pretest/chapter. This example is from the first pretest. Its kind of blurry but you will get the idea when I explain it.
So the first column on the left I have the skills I am (assessing or teaching.) I just number them to save room, I have a list of what they are in my unit plan. Then along the top are the students names. For the pretest, I know which questions match the skills so if they got them right I put the circle with the plus, most of them right but maybe 1 wrong, they get a circle with one line, if they have a clue but got the problems wrong (silly mistakes or whatever) I give them a blank circle. If they have no clue, its a blank box. So when I graded the tests, I used a red pen. The next day, I have stations for them to work at based on what they missed. They then have new problems to try as a reassessment (those I wrote in pen to the left) and I go through as they work updating my circle tracker. Those who still struggle, will get pulled for extra help during our last period which is a skill reinforcement period.
I really like how I can see at a glance if there are any major trouble spots. For example, after the pretest, I could quickly see that not one student could approximate a square or cube root on the number line, so instead of sending them off to stations, I did a mini lesson on it; that was the third skill down and so far 9 have mastered it, 2 are getting there and only 1 is still struggling.
During lessons, I start by using this with their independent practice and homework. It is really nice to keep on my clip board and reminds me to "check in" or confer with everyone. Plus if I have struggling students I want to refer to our RTI Specialist I have documentation to back it up.
I must admit, I tried using this last year and it was a little overwhelming. This year, since we are using new textbooks and curriculum mapping it is a lot easier. I finally feel that it really serves its purpose!