The International Anglican Women's Network says obstacles like poverty and a lack of education are preventing girls from achieving their full potential.
The warning came on the United Nations' first ever International Day of the Girl to overcome discrimination against girls.
This year's focus is child marriage, which the UN says affects more than 10 million young girls around the world each year.
Even in countries where the practice is illegal, girls may be forced into an early marriage and deprived of their childhood.
The International Anglical Women's Network warned that there were serious health risks, with child brides more likely to be affected by HIV and Aids, premature pregnancy and maternal mortality.
Network coordinator Ann Skamp said: "Girls are three times more likely than boys to suffer from malnutrition and are more likely to be forced into early marriage.
"Around the world, the daily realities of poverty, discrimination and violence mean that one in three girls is prevented from receiving a secondary education.
"Only when obstacles such as these are dismantled will girls properly achieve their full potential. So it’s time to shatter stereotypes, advocate for and enable equality, and change girls’ lives."
Mrs Skamp condemned the attempted murder on Tuesday of a 14-year-old school girl in Pakistan.
Malala Yousafzai, an activist for education for girls, was shot in the head on her school bus by an extremist.
Mrs Skamp said: "Today let’s hold in prayer Malala and all girls in cities, towns, villages and rural areas across our world, remembering that Jesus Christ has shown us the ultimate preciousness of each girl and each boy in our midst."
Girls still not achieving full potential
Published 11 October 2012