Write your observations in a notebook at specific times every day. It's important to follow a child's routines and get to know what he or she does approximately the same time each day. This makes it much easier to notice differences in behavior. Also record the date and the time of day for each entry, and try to use a different page for each day.
Write milestones and significant achievements as they happen. Important events -- such as losing a tooth or learning to tie shoes -- are noteworthy. Writing down these observations provides a time line of each developmental stage of a child, and can be used as references later when discussing with the parents. Denote these specific events with an asterisk or underline, or any other way to differentiate them.
Store sticky notes and pencils in convenient locations around the room, so that you can quickly write down something the child does or says that catches your attention. The more places you have a means to write down an observation, the more details and activities you can record.
Write accurate details. It's important to record as exact as possible the words you hear and the actions you observe, not just of the child but anyone in contact with him at the time of the event. Record the other person's actions and words also.
Record your notes as briefly as possible. There's no need to form assumptions or opinions. These are just notes for you to have when you discuss the child's performance and progress with their parents. The notes should also be easy to read, as you'll want to provide copies to the parents.