This guide offers advice on the assessment of the language development abilities of bilingual preschool children. A brief review of general bilingual child language development, including mixing and loss or semilingualism, is followed by a review of current assessment practices. A language assessment procedure developed for the State of California for use with bilingual preschool children is detailed. It includes making the plan, collecting information, developing a portfolio and a narrative summary, meeting with the family and staff, and developing an appropriate curriculum. This assessment process must be repeated continually as the child develops. Using such a program will require drastic reform and, with it, a restructuring of time uses, professional staff development, accountability, and the parent-school relationship. (Contains 23 references.) (NAV)