Think of how closely squeezed the sticky rice is in sushi rolls and you have an idea of how dense the classrooms can be in Japan. In the years after the war, the average class had around 60 pupils. It was then the phrase sushi zume - which roughly translates as "as jam-packed as the rice in sushi" - began to be used to describe classrooms.
Today, class sizes are smaller, but they remain of national concern as the upper limit of 40 pupils is far above the Organisation for Economic Co-operation and Development average.
Since the 1950s, parents and educators have repeatedly called for the over-crowding to be addressed. But Japan's long-ruling Liberal Democratic Party (LDP), which had an almost unbroken rule from 1955 to 2009, only budged twice, grudgingly: once in the 1960s to bring the maximum down to 45, then in the 1980s to 40.
The government's excuse for refusing to do more was a lack of money in the education budget. This would be more persuasive if Japan was not one of the richest countries in the world - number two in terms of economic might. Yet it spends one of the smallest percentages of its GDP on state education - 3.5 per cent, compared with 5.7 per cent in France.
The large numbers of pupils in a class have contributed to a trend in the last decade for classroom chaos (gakkyu hokai). These problems occur when classes have become impossible to govern.
Last August, Japan's voters gave the heave-ho to the LDP and voted in the more public-minded opposition Democratic Party of Japan. It is beginning to make good on an election promise that it would hire more teachers to thin out the classes. "About time," many beleaguered teachers will be thinking.
They may also take comfort from demographics: shrinking families are causing the school population to dwindle. But this has made little difference in recent years as schools have simply crammed all their pupils into one superclass the moment the intake has dropped below 41.
So will we see class sizes fall soon? Hopefully - but there are some parents and politicians who, incredibly, think that smaller classes may not be a good thing.
Their philosophy is that "a large group is a good group". They view themselves as a big homogenous body crammed into a tiny space (mountainous Japan) and the key to getting along is to leave individuality at the classroom door, starting at elementary school. So the bigger the class, the better prepared you will be to submerge yourself into the well-regulated classroom that is Japanese society.
However, this view flies in the face of new government policy to promote the individual, in order for the Japanese to become more creative and better competitors in the global marketplace.
Perhaps those big classrooms of passive learners made Japan what it is today - hardworking, with a strong bent for group consensus. But given that the boisterous and individually minded behaviour of young people is now making traditional command-and-control teaching nigh on impossible, the young seem to have voted already on what they think of being treated like sushi rice.