Observing and measuring early development of grammar in Spanish children. This study analyzes parental report data as a source of information about toddlers' grammatical development. It is a study of concurrent validity that compares parents' reports obtained with the European Spanish version of the MacArthur-Bates Communicative Development Inventories (CDI) with spontaneous speech measures from 35 children who took part in this study. An observational tool was developed to assess the level of grammatical development of children under 2;06. The relationship between the scores from the parental report, data from the observational tool, and the MLU (mean length of utterances) of the children's spontaneous speech were analyzed. Results show the parental report to be highly associated with the other language measures, but to differing degrees for the different measures. The implications of these differences are discussed.