Observation is a topic that can never be discussed enough. It is so beneficial for everyone involved. The child observes demonstrations by the teacher as well as the work of the other students, to learn how to properly use the materials. I cannot tell you how many times I have had a child who appears to be doing nothing but watching other children for several months. Then all of a sudden, he is replicating the lessons on his own. I still love to tell the story of one little boy who was barely four years old. He never seemed to want to do anything but build with the sensorial materials. One day, I was teaching a child how to put together phonetic sounds to make a word. The child was having some difficulty figuring out what the word said. From out of nowhere, the little boy yells the answer from across the room! He was also able to pull out the letters and do it on his own after that. And here I thought he wasn't paying attention to anything!
That also means that adults need to be on their guard at all times and to be conscious of their every word and movement. You think that you are not being watched. But there are eyes and ears on you at all times! They will mimic you when you least expect it!
Observation is also key for the teachers in the classroom. You have to observe the children to figure out what is working and what isn't working. You have to observe a child who seems out of sorts, to figure out what is going on so that you can help him. You have to observe the individual work of a child to determine if she is ready to move on to the next level. Simply "testing" a child is not enough.
We never take enough time out of our day to observe our children. I miss my loft in our old building. I could go sit up there and observe my children with an eagle eye view. I could observe the traffic patterns and see more interactions. I could closely watch a child without him realizing I was doing it. I was unable to bring the loft to our new location and it has been hard to readjust to a different way of observing my children.
I do have a tendency to observe a lot while doing something else. I am a multi-tasker. However, I also like to make it less obvious that I am watching what you are doing. It may look like I am doing the dishes, but really I am listening to how the children are speaking to each other. I have done summer gardening work at some families' homes. Sure, I may be focused on pulling those weeds, but I am also listening to the interactions in the family, which gives great insight into a child's personality and reasoning. If everyone knew I was actively observing, they wouldn't necessarily behave in a normal fashion. I know that I tend to alter my movements and actions when I know I am being watched. It is an uncomfortable feeling. That is why I try to mask it somewhat for the children.
Observation skills are somewhat innate to each individual person. You can, however, develop your skills with more practice. Write down exactly what you see. Don't worry about making judgments based on those notes while you are in the middle of observing. Review your notes and ponder those ideas later. The more you do this, you will find that it starts to happen simultaneously and you pick up on things much faster.
Here are some links to other articles I have written about observation:
10 Tips for Choosing a Montessori School
The Montessori Child as Observer
The Montessori Teacher's Role as Observer