Complex sentence: In 1849--50 they planned the rebuilding and enlargement of the Charity School for Girls in Middle Street, Lancaster, and in 1851 a new school, the National School for boys in St Leonard's Gate.
Split into simpler sentences: In 1849--50 they planned the rebuilding and enlargement of the Charity School for Girls in Middle Street, Lancaster. In 1851 there followed a new school, the National School for boys in St Leonard's Gate.