An MP has written to Education Minister David Laws asking for left-handed pupils to be guaranteed the special teaching he says they need in school.
Sir Peter Luff, who is himself left-handed, says teachers sometimes miss signs that pupils are left-handed and this can lead to developmental delays.
The government says it has introduced guidance that left-handed pupils should receive teaching to meet their needs.
But Sir Peter says this needs to be made statutory.
In his letter, Sir Peter said: "I remain deeply concerned that proper provision for left-handed pupils is not in included in the statutory guidance of the new national curriculum.
"I have heard various stories of schools that do not follow this practice at all, and as a result left-handed pupils suffer."
In an earlier speech on the issue in the Commons, Sir Peter said: "Children who have difficulty with their writing, their colouring or their cutting out, because they have been encouraged to regard themselves as right-handed, will try to avoid the activities that cause them difficulty, leading directly to slow development and under-achievement.
"Teachers need to be trained to recognise the symptoms of left-handedness, respond to them positively and help those children to use their left hands.
"Left-handed children who try to use their right hand will often cope, but that is all they will do. They will not excel as they might have done, and their development is delayed. Only if teachers are encouraged to recognise left-handedness early will that be prevented."
There have been a number of research papers suggesting left-handed pupils do worse than their right-handed counterparts at school.
In 2008, researchers at Bristol University found left-handed pupils scored 1% lower in national tests on average than their right-handed peers.
And in 2010, a study suggested left-handed pupils may underachieve in some subjects because of a lack of specialist equipment and "ignorance" of left-handedness among teachers.
The Department for Education said: "As part of the new national curriculum we have introduced guidance which is clear that left-handed pupils should receive specific teaching to meet their needs. We trust teachers to use their knowledge and expertise to cater to the needs of all of their pupils."