Some education leaders are giving an early warning that they may have to institute more protectionist policies over placing requests and ask parents if their child has needs.
Authorities such as East Renfrewshire, which attracts disproportionately high numbers of requests, fear that budgets will be hit by the new legislation's provision for the home authority to retain funding for costs such as ASN auxiliaries.
Ian Fraser, head of service for children and young people at East Renfrewshire, estimated that neighbouring Glasgow would "make a good pound;500,000" because of the changes. "It is not a pretty picture if you are in East Renfrewshire," Mr Fraser said. "But it is a good deal for Glasgow."
Around 2,000 youngsters, mostly from Glasgow, attend East Renfrewshire schools through placing requests, with East Dunbartonshire in a similar position.
Mr Fraser said: "If 20 per cent of them have additional support needs, that means an extra 400 youngsters in our schools who need extra support. We have no problem about educating these children, but they take additional resources in the form of teaching staff, special needs assistants and technology.
"Our contention is that the funding has to follow the child, but the new ASL code of practice says that if a placing request is granted we are the authority that has responsibility for that child."
It is anticipated that Glasgow's current funding of special needs assistants for 15 pupils could stop. Cross-border funding would continue as long as the pupils retain their record of need under the old system. But within two years of moving to co-ordinated support plans (CSPs) under the new legislation that funding would be retained by the home authority.
Mr Fraser said: "We will have to think very carefully about our way forward in our handling of placing requests if we are going to be responsible for the funding of them. There are inevitable consequences for what we are being asked to do.
"We can't ask council tax payers in East Renfrewshire to fund the additional needs of youngsters who live in Glasgow. We want to provide a service for these pupils, and parents are motivated to come to East Renfrewshire schools because of the level of support they get here."
Parents of children with additional support needs may now face limits to their freedom of choice, East Renfrewshire fears. Mr Fraser said: "We would be asking parents to indicate to us that their children don't have additional support needs. The classic reasons for putting in placing requests are because a child is being bullied and therefore has additional support needs because he or she is not making progress."
He predicted that parents might well take such cases to the new additional support needs tribunal or other forms of mediation or dispute resolution, and said that the council's defence against such complaints would be "unreasonable cost".