When I went in the classroom to observe, I had the teacher select a "comparison student" that I'd also monitor. The "comparison student" and "referring student" received a (+) if they were on-task and a (-) if they were off-task for each 30 second increment. (I used the "Stopwatch" on my iPhone to keep track of the time). I placed X's in the appropriate boxes to denote the problematic behaviors of the "referring student". At the end of 15 minutes, I'd count how many off-task behaviors each student received and placed it in the "Totals" boxes at the bottom of the page.
It's really an effective tool for parents to see during RtI meetings and parent conferences! If you have any other observational forms you use, please send them my way!