Uncertainty scores (H and relative H) were computed for the verbs, noun phrases, and sentences produced by 180 children between the ages of 5 and 13 years on a story-telling task. Linear age trends occurred for Sentence H and relative H and for Noun-phrase H (though not relative H), but not for verb H and relative H. There were no overall sex differences, but measure-specific age-by-sex interactions and higher-order age trends. Uncertainty scores of the type proposed, if suitably refined, may measure the developmental progression from stereotyped reliance on individual syntactic forms to flexible utilization of productive rules.