Old is covered by dust, teachers by paper. It is crucial to keep records of students so parents know what their sunshines are doing at school. Keep documents of any assessment or other behaviors so parents can have a realistic picture of their children (picture which is, of course, often inflated by parents).
Teachers have developed an extremely high emotional intelligence. They can ‘read’ a kid or other people in less than 30 seconds. What is difficult, is when this ‘assessment’ needs to be shared. When this appraisal is to be showed to others. This is something that has to be defended; it is very easy to be shaken and undone by a very supportive parent (and they often are!).
We instinctively do assessments all of the time, sometimes without even realising it. However, when documented, the paper work must reflect reality and, again, I reinforce the importance of taking notes.