As a middle school teacher, I have a hard time finding products regarding self-monitoring for older students - much of the time they are too immature for my purposes. However, lack of self-regulation skills is still an issue for many students in early to upper middle school.
This document is a streamlined, more mature version of a self-monitoring sheet for older children. This document was created to monitor on-task behavior. It also includes an area for student self-disclosure to help teachers gain some insight about what may be causing the student's off-task behavior.
I hope this document helps you teach your older students how to stay on-task and self-monitor in your classroom :)