Sarah Brown co-founded charity Their World 12 years ago with the aim of improving the early lives of children.

Ahead of International Women's Day 2015, she sat down exclusively with ELLE to discuss Up For School: the charity's latest campaign, which aims to tackle the issue of 31 million girls who don't - or rather, can't - go to school worldwide.

•    What are some of the biggest challenges that girls who aren't in education face when it comes to going to school?
Girls can face such enormous barriers. We saw it last year when we saw those young Chibok girls who were abducted by terrorists being able to force a community into keeping girls out of school. We saw it with the young Pakistani girls, Malala and her friends Shazia and Kainat, who were attacked on their school bus.

There are too many examples of that - of schools being bombed, of being used as a place to store weapons. Half of the out-of-school children are affected by conflict or are in the aftermath of a conflict.

Then girls being married off - 12, 13, 14-years-old - and not being given an education before that because their families know that’s what their future holds. And young girls working; either being sent off to bring in an income, or caring for younger children in their family.

These things are great challenges for us, but I think they’re all things the can be changed and things where, together, we can take action and call on political leaders to make a difference to girls and give them that better chance.

•    How will the Up For School campaign help to change things?
We’re aiming to ask the UN member countries who promised that every single child would have the chance of a basic education by the end of 2015 to put that into action. There’s actually no rocket science needed: nothing needs to be invented, no cure needs to be discovered. We know how to train teachers, and teachers know how to go into a classroom and teach.

Or, if it’s too hard to create a classroom, we’ve got all the opportunities that technology brings, and being able to have people learn in all kinds of different ways. What that means is, unlocking the political will, unlocking the not-huge funding that it would take to have every child have the chance to go and have a basic education.

•    What can people who want to support the campaign do to help?
The simple action that you can take right now is to add your voice and show that you care about it by signing the Up For School petition. Just log onto upforschool.org, sign - literally add your name to it - and then share it to your networks. It’s that simple.

•    What are some of the differences that Their World has already made to improve the lives of girls worldwide?
We started with a big vision that we wanted to make sure that children had the best start in life. In our early days, that meant supporting research projects around safe pregnancy, safe childbirth and investment into early years. Then we extended our horizons and looked at skill-sharing with organisations - mentoring, role models - and really investing in girls for the impact that they could make.

As we’ve grown and as our ambitions have gone wider than the UK, we now have a global set of activities. We’re really investing in young people and how they campaign and how they use their voices to make a difference to others. 

•    Why is International Women's Day so important to this campaign?
International Women's Day gives us a chance to really focus on girls, and the barriers that girls face that seem to be higher in education. It seems to take so much more for a girl to be able to go to school and then to be able to succeed and thrive beyond that. So International Women's Day reminds us of the challenges that are faced.

But we can also take stock and realise that we’ve come quite a long way. I always think there’s also a huge sense of solidarity of women helping other women and that’s what’s becoming so special about this particular day as it comes round each year.

International Women's Day 2015 is on 8 March. Find out more about how ELLE is supporting women here.