List a separate folder for the portfolio project on the students' school supply list at the beginning of the year. As the year progresses, put samples of each child's work into that child's folder. For example, you could include art projects and worksheets students have completed. At the end of the year, look through each individual student's portfolio and assess the child's development in terms of how the child has progressed through the course of the year.
Keep a notebook of your observations of each child in the classroom. You may want to assign this task to the teacher's assistant or aide so that she can jot down notes as the day progresses. Look at the different areas of childhood development. For example, note how each child responds to academic questions, but also to social situations and artistic projects. Observe how the child works in group settings as well as by himself.
You can also give preschoolers individual tests to assess their progress. For example, you could put a simple ABAB pattern down a table using blocks, crayons or other items in the classroom. See if the child can tell you which item goes next. Other options include opening up to a random page in a book and asking the child to read a random word, or asking her to count as high as she can.
With the help of the school administration and any other early-childhood experts in the school, create a developmental checklist. The checklist might be targeted at a specific area of development, for example motor skills or the ability to recite the alphabet, or it might be a comprehensive chart that accounts for a wide number of areas of development. As the student reaches certain milestones, write down the date on her individual checklist.