Children in Scotland, the Edinburgh-based umbrella group, this week urged MPs to amend the existing wording in the forthcoming Bill on disability discrimination, much of which applies north of the border.
Maire McCormack, special needs policy officer, said she was "disappointed" that the legislation would only require authorities to take "reasonable steps" to change policies, practices and procedures.
Ms McCormack said: "The phrasing of the recommendation is vague and open to interpretation. This also applies to the duty to take reasonable steps to provide education by alternative methods. We again reiterate our disappointment that schools will not be required to remove or alter the physical features of the premises.
"Modernising Scotland's schools to be fully accessible should be seen as an urgent priority since it is unacceptable for children to be excluded from schools or particular classes because of a lack of basic adaptations."
Children may not have a choice of school in rural and remote areas and their inclusion may depend on altering physical features, Ms McCormack said.
The Bill includes obligations to adapt physical features for post-16s but avoids school ducation. "This is inconsistent and unwelcome," she said.
The legislation places a planning duty on education providers to increase accessibility to schools, but this only applies to England and Wales. The Scottish Executive is expected to announce its own arrangements.
Children in Scotland is concerned that the Bill proposes rights of redress for pupils who feel discriminated against but in Scotland this will be to the sheriff court rather than the SEN tribunals south of the border.
Courts will be asked to find "an appropriate educational remedy" for school-age children. In contrast, disabled young people in further and higher education will be able to seek financial compensation. The role of the Disability Rights Commission should be clarified, Children in Scotland says.
It points out that the Bill places three new duties on schools, including making it unlawful to discriminate against disabled children by treating them less fairly simply because of their disability. Schools would have to justify their different approach.
It will further be unlawful if schools fail to take reasonable steps to change policies, practices or procedures which place disabled children at a substantial disadvantage.
Schools and authorities should also take reasonable steps to provide education using a reasonable alternative method where a physical feature places a disabled child at a substantial disadvantage.