Harvard Graduate School of Education will partner with Dimock Community Health Center and Greater Lawrence Community Action Council Early Head Start (EHS) and Head Start programs to pilot, refine, and validate instruments to be used to track children's vocabulary skills in English and Spanish over time, as well as their changing exposure to and use of each language at home and school. Specifically, the project seeks to: (a) demonstrate the validity of the MacArthur Communicative Development Inventories (CDI) English and Spanish Toddler Short Form for use by parents and teachers of EHS and Head Start children; (b) pilot and validate a Spanish adaptation of the English CDI-III, and extension of the CDI vocabulary checklist intended for older preschoolers; (c) ascertain the age range for which each checklist is appropriate; and (d) refine parent and teacher questionnaires about children's exposure to and use of English and Spanish at home and school. Participants will be EHS and Head Start children between the ages of 24-48 months and identified as Spanish-speaking English Language Learners, their parents and their teachers. Pilot data on 40 children and families will be collected during Year 1. Data will be collected during Years 2-3 on 120 children. The instruments designed in this study are expected to provide a concise set of 'snapshots' of an individual child's exposure to, use of, and vocabulary skills in both English and Spanish over time.