Schools in England are being advised on how to stop the bullying of children with special needs or disabilities.
Schools Secretary Ed Balls says bullying of this kind is the "cruellest expression of cowardice".
The charity Mencap says eight out of 10 children with a learning disability have been bullied, and six out of 10 physically hurt.
The government says evidence shows that children with special educational needs might be more isolated.
They might find it harder to resist bullies and to tell someone about it.
Bullying children with special educational needs and disabilities has to be the cruellest expression of cowardice
Ed Balls, Schools Secretary
The guide was launched at a conference, Aiming High for Disabled Children, by the schools secretary.
Mr Balls said: "Bullying children with special educational needs and disabilities has to be the cruellest expression of cowardice. Singling out a child because they are different is unacceptable and wrong.
"We all need to look beyond the disability and see the young person.
"According to Mencap figures eight out of 10 children with a learning disability have been bullied and six out of 10 physically hurt.
"That means they're twice as likely to be targeted than other children. I find that utterly deplorable and something we must all work to put a stop to."
Official figures suggest around 1.5 million of the school population, almost one in five, have a special educational need and that more than half a million children have a disability.
The guidance follows specific advice to schools about racist and homophobic bullying.
General secretary of the Association of School and College Leaders John Dunford said: "Schools work hard to create a climate of tolerance and understanding, especially for those with a physical or mental disability.
"Bullying in schools is taken very seriously, especially when it involves vulnerable pupils. The guidance will be useful in reviewing and improving strategies to deal with the particular issues of this type of bullying."
Emma-Jane Cross, head of Beatbullying, said she welcomed the guidance - but more action was needed.
"In particular, Beatbullying is delighted that the government recognises the importance of prevention in tackling the problem, and that it is not just the responsibility of teachers, but also parents, young people, and the community in general, to build an understanding of what is and is not acceptable behaviour.
"However, anti-bullying guidance and recommendations will only have a limited impact. Beatbullying is disappointed that, despite the large amounts of money rightly allocated to disabled children’s services and projects, the government continues to show a lack of commitment to funding bullying prevention work in every school."