Focusing on English, the predictions of this compositional approach to factivity are tested with production and comprehension data covering children's acquisitional patterns between the ages of 2 and 8. After a comprehensive review of previous studies, the author presents two rigorously designed comprehension experiments and a detailed analysis of two longitudinal corpora. The child data provides convincing evidence that the multidimensionality of factivity is mirrored in the acquisition process by a stepwise mastery of its different components. Children produce and correctly interpret factive structures around age 4, but certain syntactic and discourse-semantic properties are not learned before age 7. This book should be of interest to advanced students and researchers in both theoretical linguistics and language acquisition.