In the coolness and golden light of a late afternoon – with Mount Moroto, part of a volcanic chain, in the background – a dozen girls sit beneath a tree. They are playing board games, but there is serious intent behind the activities.

It's been 13 years since the girls and their community moved to this picturesque setting in Lotede, just off the dirt track that passes for a main road and leads to Moroto, the main town in the remote north-eastern region of Karamoja in Uganda. They arrived, from 40km away, after 1,000 armed men attacked their village, stealing 2,000 cattle.

The 600 villagers, who live in thatched huts with conical roofs, subsist by growing maize, bananas, cassava, sweet potato and sorghum. The recent rains mean the landscape around the village is green, which makes cultivation easy since the soil here in southern Karamoja is rich and fertile. With just a tiny airstrip in Moroto, Karamoja is accessible to most people only through a 420km road from the capital, Kampala, that is full of ruts and potholes.

Karamoja is Uganda's poorest province. It was once the scene of cattle rustling, with the various clans – including the Matheniko, Gei and Dodoth – of the Karamojong people stealing from and ambushing one another using guns looted from armouries after the fall of Idi Amin.

The violence meant the area was off-limits for a long time. But in the past few years, government officials and NGOs have moved to tackle the poverty that afflicts the population of 1 million scattered across 27,900 sq km of semi-arid terrain.

Early marriage – as young as 13 – and early pregnancy are common. Uganda has the world's second youngest population, with 78% below the age of 30 and 60% under the age of 20. The unemployment rate among 15- to 24-year-olds is 62%. More women are unemployed than men, with younger women particularly affected.

According to Unicef, the UN children's agency, between 1990 and 2010 Uganda had the fifth highest annual population growth rate in the world. The country also had the second highest fertility rate globally, with 6.2 children per woman, in 2011.

To tackle early pregnancy, Brac, the Bangladeshi NGO now working in several African countries, established youth clubs in Uganda for girls aged between 13 and 21. The afternoon clubs, set up with the consent of village leaders as part of Brac's empowerment and livelihood for adolescents (ELA) programme, provide a forum for girls to socialise, write songs and poetry, and play games. They also facilitate the discussion of issues such as rape, family planning and contraception, HIV and Aids, and menstruation.

The overriding message is that early marriage and early pregnancy ends in poverty. A mentor – a girl selected from the community, and trained by Brac – heads the group discussions. It is a significant responsibility; the mentors are young, mostly in their late teens.

"I teach girls life skills, tell them they should not marry when they are still young as they will have many problems," says Agnes Lotuko, 22, a mentor at Lotede. Her responsibilities include countering the "fairy stories" that some families tell girls who want to use contraception. "They tell the girls that it is bad to swallow the pills and they will never have children," she explains.

Addressing the issue of rape, mentors urge girls to avoid "lonely places" and walking alone in the dark whenever possible. Another key message is to avoid peer groups that pressurise girls to have sex at an early age.

As of last year, Brac had established more than 1,200 clubs, reaching about 50,000 girls in Uganda. Besides sex education, the clubs teach the girls financial literacy, tailoring, and agricultural and other skills.

In Bungokho, a village surrounded by banana trees near the bustling town of Mbale, the local youth club offers microfinance. Nambuya Mloajuma, 19, a single mother with a two-year-old child, has used her time there to further her doughnut business.

"I get up at four and cook for four hours. I have saved 180,000 Ugandan shillings (£45) and need 500,000 to open a small bakery shop," says Mloajuma, explaining that the father of her child – she became pregnant while at school – "doesn't want to know".

The feedback from ELA, based on tracking 4,888 girls and young women over two years, has been encouraging. Before the programme, only 6.5% of girls reported being self-employed; afterwards, they were 32% likelier to be working.

The use of condoms also increased. Initially, 51% of the girls across Uganda – 11% of whom had at least one child – said they always used them. Under the ELA programme, however, condom use increased by 50% and the probability of young women giving birth fell by 26%. Most noticeably, the share of girls who reported having had sex against their will last year dropped from 21% to almost zero.

Vincent Namanba, Bungokho's third most senior man, has noticed a change in the village. "There were so many adolescents running around with nothing to do," he says. "Now young mothers are no longer isolated, there is a sense of belonging – and I am surprised to see so many people going into business for themselves."

Brac does not yet have feedback from its youth clubs in Karamoja, but Lotuko, who has been a mentor for two years at Lotede, gives an indication of the challenge she faces. "There are 30 girls in the club," she says, "and I tell them 'don't marry when you're still young', but 15 of them are already married."