Literacy charity Beanstalk is joining children's charity group Coram to "pool resources and expertise to make a positive difference for more children".
Coram Beanstalk aims to provide consistent, one-to-one literacy support to children across the country.
Last year Beanstalk helped 13,400 children in 1,200 schools across England through the support of approximately 3,700 reading volunteers.
Under the new banner, it will continue its programme of recruiting, training and supporting volunteers.
Ginny Lunn, chief executive of Beanstalk, said: "By joining the Coram group, we will ensure that our commitment to helping every child to gain the reading skills and confidence to reach their true potential can be realised with greater impact and security.
"By working together we can extend our work into new areas so that we can reach even more children who need our support."
Coram's chief executive Dr Carol Homden said that the new charity would combine strengths to "support schools in helping children to thrive".
Staff from Beanstalk's previous office in the Barbican have now moved to the Coram Campus in Brunswick Square, London.