And the researchers showed that a child's social background was a very important factor when it came to whether he or she would be sent to a university track school, or Gymnasium.
Scientists who examined data from recent international primary school test results concluded the most important thing was for the teaching to be good, and for additional support lessons to be provided to children who were struggling.
“An effect from class size is not demonstrable,” the researchers write in their analysis of the 2006 data, reported in Der Spiegel on Saturday.
Working under the Dortmund educational researcher Wilfried Bos, the group examined a number of different factors including the social status of parents, and the recommendation of a school of whether a child should go to Gymnasium.
They confirmed the results of other studies which suggested that children from higher social classes had clearly better educational chances than those from worker families.
The chances of a child from a higher social class going to Gymnasium are around four times those of a child from a working class family, they said.
Even when the children have matching scores in reading and other capabilities, those from a higher social background are on average still three times as likely to get into a Gymnasium than those from a lower social class, they concluded.