One method of observation is to collect each student's work in a portfolio over the course of a school year. Each piece of work should demonstrate some skill that the child has or is mastering. For example, it might demonstrate cutting or writing skills. Later, when assessing the child, you can look back at the work and see how the child has progressed. It is also useful to share during parent/teacher conferences, as you can demonstrably show how the child is doing in preschool.
Anecdotal observations are written descriptions of events witnessed in the classroom. Keep a notebook with you during the day and write short notes about what you see the students doing. Later, at the end of the day, you can expand on these notes. Collected together, anecdotal records will give a picture of what each student does during the day, and how her behavior, play and learning have changed over the course of days, weeks or months.
Sometimes you simply wish to know whether a student can accomplish a developmentally appropriate skill and when that child was first able to do so. Checklists help with this. Make a list for each child of all the developmentally appropriate skills you wish to chart. When you see a child performing that task, mark it down on his checklist by writing down the date you observed it. This will give you a snapshot of where each child is developmentally and help you plan classroom activities.
Frequency counts record how often a certain event or activity is occurring. Perhaps you want to know if a child is playing in one area most of the time or is playing in several different areas. Or, perhaps you are wondering how often certain play problems are occurring. By keeping a running tally of these things throughout the day, you will better know whether these are issues that need to be addressed.