Students learn the importance of a teacher look because in the moment it's a non-verbal communcation between the teacher and the student. It's important to have a teacher look so that way the teacher isn't constantly addressing unwanted behavior infront of the whole class. Giving the teacher look to a student provides them another opportunity to make a better choice.

Students have been getting the "teacher look" from probably every teacher they have ever had, they know it is a gentle nudge to get them back on track.  I think it's important to have one to keep distractions in the classroom as minimal as possible and it shows respect for the child and allows them choice to get back on task without other interaction from the teacher.

The teacher look is important because you want the student to know that they need to redirect their behavior and you are giving them a chance. Students learn the importance of this look because they need to know that they have another chance to make a better choice but they were given a warning. An effective time to use this strategy is when a student needs a reminder of the expectations. They suggest that every teacher has this look to provide a quick and easy warning signal. 

Definitely understand the teacher look. It is very similar to a "Mom Look". By using this method, correction in behavior can made without getting to a public call out. I know I've received this look before 

Interesting how looking at a student in a certain 2way can facilitate more focus and on-task time.