Benjamin, an ethnic Albanian, and Luka, an ethnic Serb, are young neighbours who share a school but meet only on the football pitch. One boy is taught that Kosovo is independent and the other that it is a Serbian province.
In the former Yugoslavia, especially Bosnia, Kosovo and Muslim-dominated areas of Serbia, schooling is often determined by ethnic affiliation.
"In the long term this will cause social damage and political instability," said education specialist Dukagjin Pupovci, warning that Serb pupils in Kosovo risked living "outside reality".
Kosovo declared independence from Serbia in 2008, a decade after a war between its ethnic Albanian pro-independence rebels and Belgrade forces.
Although more than 110 countries now recognise Kosovo's sovereignty, the ethnic Serb minority in the former province does not and is backed by Serbia and Russia.
In Palaj, on the outskirts of Kosovo's capital Pristina, a slim majority of its 400 inhabitants are ethnic Serbs who call the village Crkvena Vodica ("Holy Water").
They share a school with the local Albanian community, but the name of the establishment changes according to class ethnicity.
In the morning, when the school hosts around 50 young Serbs, it is called "Dositej Obradovic" after an 18th century Serbian writer and philosopher.
But in the afternoon, when some 80 Albanians take to their desks, it is known as "Fazli Graiqevci" in honour of an Albanian education activist.
Benjamin, a Barcelona fan, meets Real Madrid supporter Luka only when playing football.
"Everyone speaks his own language. When we do not understand each other we speak using our hands," 11-year-old Benjamin told AFP.
Luka, 12, said there were rarely any problems, and if they do occur, "we solve them by ourselves, we don't call our parents or teachers".
While their parents often speak each other's language, a legacy of the former Yugoslavia, the two young boys do not.
Benjamin can learn English and French at school, while Russian is the preferred second language for Serbs.
"We are like two trains arriving from different directions and meeting only briefly at the same station," said physics teacher Sejdi Preniqi.
This is above average integration for schools in Kosovo, where the two ethnic groups typically learn on completely different premises, with the Serb system and its teachers funded by Belgrade.
The Albanian students arrive half an hour after their Serb counterparts leave, so there are "no problems" according to Igor Maksimovic, head teacher for the morning intake.
In the school corridors there are no national signs. "We don't deal with politics," said Maksimovic.
"They work with their programmes, we work with ours, it does not spark any tension," said his ethnic Albanian counterpart Mevlude Greicevci.
Such segregation also exists in Bosnia, where Bosniak Muslims, Orthodox Serbs and Catholic Croats live alongside each other with little integration.
After the country's 1992-1995 inter-ethnic civil war, which claimed about 100,000 lives, the state was divided into two semi-autonomous entities -- the Serb-run Republika Srpska and a Bosniak-Croat federation.
The country is home to just 3.5 million people, yet services including postal systems, electricity and education are separated for the three main ethnic groups.
But at a secondary school in the central Bosnian town of Jajce, Croat and Bosniak pupils have rejected this separation. More than 500 youngsters from the two communities learn together.
Ruins of houses destroyed in the war can be seen from a window of the school, but graffiti on a wall of the white building reads "Zajedno stvaramo" ("We create together").
Last year the authorities decided to move Bosniak students to a separate establishment -- a decision met with resistence from Azra Keljalic, born six years after the conflict, who started a petition to "stay together in school".
Keljalic said she does not identify with any community and did not want to talk about her religion.
Backed by Western embassies, she and her friends made the authorities change their decision, but their victory was only partial.
The new students enrolling at the Jajce school will be separated during history and geography classes, which is already the case for religious studies and language lessons.
"We continue the fight for... a single curriculum," Keljalic said.
At her primary school, she recalled, "we could not be together, even in breaks. Everything was separate: classes, staff rooms, even the garbage cans.
"They poisoned us with these divisions in the period of life when one absorbs most things."
Nikolas Rimac, 18, also campaigns against what he calls a "catalyst of the hatred to come". He refuses to define himself as an ethnic Croat and attends Bosnian language classes.
"There they teach about some great writers whom they don't tell us about in Croatian classes."
The state's three official languages -- Bosnian, Croatian and Serbian -- are so similar that many say they are the same, provoking the anger of nationalists.
Amela Kavazbasic, a teacher at the Jajce school, expressed pride in the students "who have decided not to accept something imposed on them by politics".
But such initiatives remain rare.
"Nationalists have seized education and use it as a tool of indoctrination," said Nenad Velickovic, a literature professor at Sarajevo University.