A key factor in determining a child's level of reading achievement is the amount of reading experience. More reading experience contributes to vocabulary growth, and vocabulary development facilitates reading comprehension, an example of reciprocal causation. This reciprocal causation leads to the rise of Matthew effects: children who have strong vocabularies and reading skills read more, and continue to improve their vocabularies/reading skills, whereas children with weak vocabularies and poorer reading skills will read less, hindering the development of their vocabularies/reading skills.