In the small West African country of Sierra Leone, 46% of girls and young women aged 15-24 do not know how to read and write.
In contrast, 72% of Sierra Leonean boys and young men are literate (UNICEF).
Isatu, who is now 17 years old, dropped out of secondary school in Year 8 because her family could not afford to keep her there. Year 9 is the last year of basic education in Sierra Leone, and her family knew they would not be able to afford the end of year exam.
Sierra Leone is missing out, because when girls and women are educated, everyone benefits. Women who reach secondary school earn more, have fewer and healthier children, and are more likely to send their own children to school (World Bank).
Currently, Sierra Leone has the highest maternal mortality rate in the world.
Today's UN Day of the Girl Child is a global reminder that we need to listen to girls, understand their problems and take action to make life better for everyone.
Street Child, an NGO working to help some of the world's poorest children to access education, recently carried out a nationwide consultation with two thousand adolescent girls across Sierra Leone. Its aim was to understand what stops girls going to school. National researchers in towns and villages across Sierra Leone conducted the survey with girls both in school and out of school.
Researchers spoke with girls like Isatu who is from Bo, one of the largest towns in Sierra Leone.
Isatu's story was common - poverty was found to be the major principal barrier to girls' education in Sierra Leone - over 40% of out of school girls said that was the reason they dropped out of school. In households with very meagre resources, education of girls is often not prioritised.
Isatu now helps her mother to sell snacks in the market. On a good day they make £3 profit, which supports a family of ten.
Over 70% of Sierra Leoneans live on less than £2 a day.
Barriers to education for girls are often inter-linked. Isatu herself comes from a single parent family, since her father died when she was 13.
The loss of a caregiver, and the accompanying financial and emotional trauma, was the second most common reason for girls dropping out.
In these situations, girls are often required to take on the role of caregivers and breadwinners themselves. Street Child estimates that the recent Ebola epidemic saw 12,000 children orphaned in Sierra Leone alone. Many orphaned girls are now trying to earn a living and take care of younger siblings instead of going to school.
Although Isatu's mother says she wants her daughter to go back to school, she also said she needs her help with the business and looking after the children. Three out of the five girls in the family are not in school.
Isatu's three brothers are all still in school.
Adolescence is a critical time for girls in school in Sierra Leone. Responsibilities for child care and income mount; and the risk of child marriage and teenage pregnancy increases with physical maturity.
During Ebola, many girls became teenage mothers, often because 'boyfriends' would offer them with a little money to buy essentials like food.
Isatu become a mother a year ago - her little daughter Marie was born when the Ebola crisis was at its height. Both Isatu and Marie were fortunate; Sierra Leone is one of the most dangerous places in the world to give birth. And according to one study (LSTM, 2015) maternal mortality during Ebola rose by 30%, due to fear of health facilities and lack of basic education.
But Marie's father disappeared when he found out Isatu was pregnant, and she receives no support from him. When girls drop out of school because of teenage pregnancy - the third most common reason - they very rarely go back.
Isatu is very keen to finish her studies, and she is not alone. There is a huge appetite for learning amongst Sierra Leonean girls. Over 80% of the out of school girls interviewed said they wanted to go back to school.
The support of boys and men is critical for girls' education. The National Consultation interviewed both boys and elders, and found a lot of support. Yet the misconception that girls are not worth educating as much as boys was often repeated. "Girls are for the marital home in the end", they said, "they have weaker brains".
The national statistics show how this ends: for every two boys that reach the last year of secondary school, only one girl makes it (UNICEF, 2014).
Neither of Isatu's parents ever went to school themselves - illiteracy is even more common amongst the older generations in Sierra Leone. But because Isatu got as far as secondary school, her daughter Marie is more likely to go to school herself.
When girls like Isatu miss out on education - Sierra Leone misses out too.
International Day of the Girl Child is about standing with girls like Isatu so that she can create the future she wants for her daughter.
It serves as an important reminder to all of us to examine gender inequality in our own communities and our global community. Tackling these problems won't just benefit girls, it will benefit everyone.
The road to global gender equality is going to be a long one - but it is worth the fight.
Megan Lees-Cowan is Street Child's Director of West Africa Programmes. She is based in Freetown, Sierra Leone
Street Child is a UK NGO working in Sierra Leone, Liberia and Nepal. Street Child's recent 'Girls Speak Out' Appeal was match-funded by the UK government and will enable 20,000 children - especially girls - to go to school in post-Ebola West Africa.
Find out more about the work of Street Child, click here