Algebra is a universal language.
A rosy-cheeked young teacher is instructing her class in the finer points of x and y and attempting to explain just what to do with those pesky brackets.
But that's about all that's familiar in this classroom. The teacher is speaking Korean and wearing the traditional dress of North Korea.
She reaches up to write on the blackboard directly under two portraits on the wall. The smiling faces of the late North Korean leaders Kim Il-sung and Kim Jong-il look down on her class of 16 and 17-year-olds.
But this is not downtown Pyongyang — it's Tokyo.
The portrait of the current North Korean leader Kim Jong-un hasn't been added to the wall… yet.
The school says he hasn't made a statement specifically acknowledging the North Korean community in Japan, but if he does, his portrait will be added.
Dean of studies Kim Seng-fa says the school was established in 1945 by the Korean community in Japan, many of whom had been forcibly removed from Korea to become labourers in Japanese factories.
"They didn't want their children to grow up in Japan without knowing their native language. The Korean School started as people wanted to learn the Korean characters, culture and customs," he said.
Seventy-one years later, the school is a strange place.
The students speak of Korea as a "motherland" and seem to ignore the fact that it was divided after the Korean War.
As well, they say Kim Jong-un is a good leader, not a dictator, and reports about human rights abuses are just Western propaganda.
Koreans living in Japan face discrimination
Sixteen-year-old Chong Soni said North Korea was being misrepresented to the rest of the world.
"I think all the Japanese media coverage is wrong," she said.
"I've been to Korea once and the country was nothing like what it's being shown in the media. Japanese media only says negative things and I think they're wrong."
Many Koreans living in Japan face discrimination.
Japan does not allow for dual citizenship and makes would-be citizens renounce the country of their forebears.
Successive South Korean governments have also made life difficult for expatriate Koreans who want to live in another country, but want to hold on to their South Korean passport.
Gesturing to the portraits on the wall, Chong Soni said many people in the Korean community in Japan "feel" more North Korean.
"These two leaders helped us when we were having the most difficult time in Japan. So our Korean compatriots living in Japan consider North Korea their home country," she said.
Seventeen-year-old Ryong Chi Hyon agreed with his classmate.
He said he was only a little bit concerned about the possibility of a war on the Korean peninsula.
"Recently, they've been testing missiles and I think the technology is developing. I hope North Korea will work hard to further develop our nation," he said.
"Nations like the US which North Korea is confronting has technical strength, I hope North Korea will develop more technology so it can defend itself from those nations."
Teacher Mr Kim said he allowed the students to think for themselves and does not teach that Kim Jong-un is an unelected dictator.
"In my mind, I don't really see it as a dictatorship," he said.
"Mr [US President Donald] Trump is coming to Japan as a state guest. It's good to talk with many people about how to resolve the issue in the Korean peninsula but we don't want him to talk about how to put pressure on [North] Korea."