Conduct research. Whether you are an academic or a childcare professional, if you want to develop your own ranking scale for preschoolers you must first have plenty of time to observe and interact with preschoolers. Most existing preschool rating scales are "norm-based" meaning that rankings are based on what is considered average for children at a specific stage of development. For example, a four-year-old will be ranked based on what is average for four-year-olds generally.
Determine what factors you will be using to rate the children. Factors do not need to be strictly academic as rating preschoolers on their interpersonal interactions, behavior, and emotional development is extremely important for determining their readiness to enter kindergarten.
Develop the language for your rating scale. It is important that the language you use in your rating scale is not too complicated so that it can be understood easily by parents and others who are not in the early childhood education field. It is also important to be diplomatic because children and parents can be sensitive. Choose your words in a way that is honest but positive.
Submit for peer review. When trying something new in a field like education, it is always best to get feedback from others in your field before moving on. This can help you fine tune your work and lends credibility to you new rating scale. In an academic field peer review can mean submitting your work to a journal or other trade publication. If you like you can also consult other professionals you work with to get their opinions before you begin using your new rating scale.