There is a wealth of research on the topic of how brain development plays a role in intelligence. Studies have shown that IQ can be predicted by brain size, white matter connections, and cortical thickness. In addition to these findings, studies have also shown that physical factors such as injury or illness can affect the brain and lead to reduced intelligence levels. Schools today are not doing enough to focus on how physical factors affect the development of a child's brain and mind. Physical activity is not emphasized in schools enough which could mean a reduced IQ for children who do not get enough stimulation from their environment.