Li Jiajun stands with her blind 12-year-old son in the rain. She is canvassing for a disability advocacy group by giving commuters free cups of green bean soup. To Li, the volunteer work is a subtle way of protesting against institutional discrimination against children with special needs. Mainstream schools cannot accommodate her son's disability; special needs schools would prepare him only for jobs such as a masseur or piano tuner.

"My son's abilities are really strong – his critical thinking and logic are even better than other students," said Li, who requested the use of a pseudonym to protect her identity. "But how could regular teachers interact with him? I just don't know."

China's official accounts paint a cheery picture of the country's disability programmes – enrolment in primary schools is widespread and there are ample special needs schools. Yet the government's policies contradict its stated commitment to providing equal access to education, according to a report by Human Rights Watch (HRW), published this week.

"Children with disabilities have the right to attend regular schools like all other children, and are entitled to support for their particular learning needs," the New York-based group's China director, Sophie Richardson, said. "But instead, some schools fail – or simply refuse – to provide these students what they need."

Even if disabled pupils complete their ­compulsory education, colleges require them to undergo physical tests and are permitted to reject them based on the results. Photograph: Don McPhee for the Guardian

China is home to at least 83 million people with disabilities, 40% of whom are illiterate. About 28% of children with disabilities are not receiving the basic education they are legally entitled to, having been barred from enrolling in mainstream schools until they show an "ability to adapt".

The report, As Long as They Let Us Stay in Class, is based on 62 interviews conducted in China between December 2012 and May 2013 – mainly with children with disabilities or their parents – and reveals a gulf between the government's promises and its actions.

In 2008, the Chinese government ratified the convention on the rights of persons with disabilities, an international treaty drafted by the UN that obliges China to provide equal access to education for children with disabilities. The same year, it passed the law on the protection of people with disabilities, which "pledged greater funding for the education of people with disabilities", HRW said.

Yet many schools fail to accommodate the needs of their disabled students, and some simply turn them away. Even if disabled pupils complete their compulsory education, colleges require them to undergo physical examinations and are permitted to reject them based on the results.

"For the Chinese government, it's important to be seen as doing quite a lot of things for people with disabilities – and it has done quite a few things," said Maya Wang, a researcher at HRW's Asia division. "The problem is it has not gone far enough, or put its resources and effort in the right places."

Children who are enrolled in special schools are frequently separated from their parents at a young age, according to the organisation. Many parents do not even know the schools exist.

"It is often the parents themselves who don't know that their children have equal rights," said Wang. "And at mainstream schools, the teachers there don't know about teaching kids with disabilities. They have very little support, very few resources, very little training."

Mainstream schools typically place the burden on the child to adapt to their environment, claiming that the school is "normal" and ill-equipped to change. Many have expelled disabled students because of inadequate performance.

The HRW report includes testimonies from students with disabilities and their families. A nine-year-old boy with attention deficit hyperactivity disorder was turned away by a public primary school; a disabled 13-year-old girl could not attend a school because it was too far from her home; a medical college refused to admit "students with disabilities in the torso or the limbs".

"Human Rights Watch found little to no accommodation in mainstream schools for these students at all stages of education," said the organisation. "One parent was explicitly told by the school that since her child is in 'a normal environment', it is the child with the disability who must adapt, not the other way round."

• This article was amended on 16 July 2013 to correct the name of HRW's China director and clarify the proportion of children with disabilities missing out on education.