Like many teenagers in her village, she struggles to pay her school fees.
A rich man has offered to pay for her education. However, in return Agnes must sleep with him.
"The man told me he would pay my school fees and everything I want," she told the BBC.
Agnes is not alone. Nine out of 12 girls in her class say they have been approached by so-called "sugar daddies".
"He told me he would pay for my school fees, pay for me to go on holidays to go to other countries" says one girl.
"When you go to his place, you have sex with him," says another girl.
Their teacher Daniel Okello says many of these sugar daddies are infected with HIV.
Girls who agree to have sex with these men are at risk of catching the disease.
However, many are trapped in a cycle of poverty and cycle and feel unable to speak out.
"The men don't have any protective measures," he says.
A local organisation called Straight Talk is helping to spread the word about sugar daddies and HIV.
It has staged marches through villages and towns in Uganda to inform teenagers about the risks.
It has already helped to convince at least one teenage girl not to strike a deal with a local sugar daddy.
"They advise us to stay safe and to stay away from those sugar daddies," says Agnes.
She has taken their advice on board. Agnes now does odd jobs to pay her school fees.