 Born Lilian Passmore, Sanderson attended Barnstaple Girls' Grammar School in Devon, before graduating in 1947 with a BA (as an external degree) from Exeter University College.In 1948 she obtained a Diploma of Education (DipEd), also from Exeter, and in 1962 an MA from the University of London for a thesis entitled "A history of education in the Sudan with special reference to the development of girls' schools".In 1966 she was awarded a PhD, also by the University of London; her thesis was "Education in the southern Sudan, 1898–1948".