According to a charity organisation, stigma and misinformation about disability, as well as a lack of data on the numbers of disabled children are causes for the problem.
About half of the world's 65 million school-aged children with disabilities are out of school due to a lack of funding, a rights groups said in a report on Monday.
The report, published by the International Diasability and Development Consortium said a lack of schooling and employment for people who have disabilities causes billions of dollars of potential income from the world's poorest countries to be lost.
Speaking about the report, Handicap International's inclusive education technical advisor, Julia McGeown said, "Children with disabilities are constantly left at the very back of the queue, and the impact on both individuals and economies can be disastrous."
Stigma and misinformation about disability, as well as a lack of data on the numbers of disabled children are causes for the problem, a charity which supported the research said.
"People don't see them (children with disabilities) as a worthy investment," adviser for inclusive education at Light for the World, Nafisa Baboo said.
"Many think for example that there's no point investing in their education as people with disabilities can't work."
The exclusion of children with disabilities prevents the Sustainable Development Goals (SDGs), which aim to ensure inclusive and equitable quality education for all by 2030, from being met, a report by the International Disability and Development Consortium said.
"The SDGs give governments an opportunity to up their game," said Baboo, adding that donors should prioritise efforts to reverse the decline in aid for education.
The education sector globally has been greatly underfunded, and international aid to education is on the decline, according to a report by the UN education and cultural agency UNESCO in September.
The new report calls on governments to provide facilities for the education of disabled children within a mainstream system.
"Inclusive education can drastically reduce out-of-school populations, it can tackle discrimination in society, and it is considerably cheaper than segregated education," said Baboo.