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Admissions rules should be altered to ensure twins are allocated places at the same school, the Chief Schools Adjudicator is expected to say.
Under the current system, each twin's application is dealt with separately by the local authority, which can mean they are split and sent to different primary schools.
About 100 sets of twins in England are affected each year, according to the Twins and Multiple Births Association (Tamba).
Many more are allocated different primary schools, but their parents win an extra place at one school either before or at appeal. Other families opt to educate their children privately, Tamba said.
Schools Secretary Ed Balls asked the Chief Schools Adjudicator, Dr Ian Craig, to look into the issue earlier this year, saying the situation was "ridiculous".
Dr Craig's findings will form part of his annual report, which is due to be published on Monday morning.
Tamba chief executive Keith Reed said the problem was down to an "oversight" in the code.
"We have conducted our own research and what we have found is that about 100 sets of twins appear to be split up each year, which causes a number of practical, emotional and development problems for the twins involved.
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"We are hoping that the report confirms that this is a problem that exists and recommends that it should be resolved by making amendments to the school admissions code."
Mr Balls also asked Dr Craig to look at fraudulent or misleading applications, to see if parents are breaking the rules and if the problem is bigger than originally thought. And Dr Craig was asked to consider whether the use of lotteries is a fair way to allocate school places.
