Kroll used the four phases to give an explanation and generalise about the development of these two aspects of language. The highest significance is placed on the second and third phase, consolidation and differentiation respectively. It could be concluded that children's written and spoken language, in certain respects, become more similar to age, maturation, and experience; however, they are also increasingly different in other respects. The content of the skills are more similar, but the approach used for both writing and speaking are different. When writing and speaking development is looked at more closely it can be seen that certain elements of written and spoken language are differentiating and other elements are integrating, all in the same phase.