Parent agencies joined forces with special needs experts to call for a tightening up of some definitions in the draft Bill so that children currently catered for do not fall through the net.
Contact a Family Scotland, a support agency for children with special needs, went so far as to predict that up to 50 per cent of families who at present enjoy legal rights could see them removed.
The organisation says, in its paper to MSPs on the equal opportunities committee, that this is because the proposed co-ordinated support plan (CSP) which will provide extra help for pupils will only kick in where an education authority has to call on other agencies.
This could point to 10,000 plans being issued, as opposed to the 17,000 children who now have a record of needs, which the CSP replaces.
Enquire, the national advice service for special needs, suggests that pupils such as those with autism or dyslexia, whose needs can be met within education authorities, may lose out by not being eligible for a support plan. Yet its database showed that, from May to October this year, 38 per cent of cases where a record of needs had been opened related to such children.
Barnardo's Scotland is also concerned that "those who are currently supported will receive less support as a result of this legislation". The integrity of the new system will depend on meeting the needs of those assessed as requiring additional support, and it urges that the opt-out clause that support must be "practicable" be clarified.
The potential for the CSP to become "less responsive and more bureaucratic" despite the intentions behind the Bill is another of the concerns of Barnardo's, particularly if only written requests to open a support plan are to be allowed.
The ability of education authorities, social work departments and health boards to work together also came under scrutiny from those giving evidence. They should be planning ahead now, the Disability Rights Commission told the parliamentary education committee.
But the Government also had to ensure that the "significant shortage" of professionals in speech therapy and social work will be overcome. "The Commission would also point out that the corollary to better entitlement will be the greater need of services and there is concern that the supply side may not be able to meet the needs that are demanded," it says in its paper.
Both the Commission and Enquire set some store by the proposed new code of practice which it hopes will ensure parents do not face a lottery when it comes to the opening of a support plan.
The Commission is concerned, however, that youngsters deemed disabled under the Disability Discrimination Act might not receive a CSP if their needs are not regarded as "complex or multiple".
The Parliament's education committee also heard specialist evidence this week from representatives of mediation and tribunal services. There was general agreement with the Scottish Mediation Network that the new service, which aims to help parents resolve disagreements with education authorities, must be seen to be impartial, and that this may not be the case where councils operate their own in-house mediation operation.
There is also growing pressure for the tribunal, which will be set up as an appeals mechanism where parents and authorities cannot agree, to be given powers over health boards and social work services as well as education authorities.
The Scottish Committee of the Council on Tribunals noted: "The tribunal might make an order that a child receives services from, for example a health board, yet the tribunal has no power of direction over that board to ensure that its decision is implemented.
"There is a danger that decisions can become meaningless," it states.