A study at The Institute of Education (UCL 2013) found that children who read for pleasure made more progress in maths, vocabulary and spelling, between the ages of 10 and 16, than those who rarely read. 
Further research (OECD report 2010) found that parents reading books with their children had the greatest effect on performance in school generally AND that the highest achieving children receive encouragement with reading well into their teens. 

More recently, a study by the National Literacy Trust (2018) found that “Children who are the most engaged with literacy are three times more likely to have higher levels of mental wellbeing than children who are the least engaged”.