Perera conducted a survey and her view mirrors that of Kroll to the extent that she used Kroll's four phases. When a child undergoes initial learning of the written language, they have not yet fully mastered the oral language. It is clear that their written language development is aided by their spoken language; it can also be said that their spoken language development is aided by the development of their written language skills. Kantor and Rubin believe that not all individuals successfully move into the final stage of integration. Perera is also aware that it is hard to assign chronological ages to each phase of writing development, because each child is an individual, and also the phases are 'artificial'.