Provisions set out in the Children and Social Work Act 2017 require all councils to be part of an agency by 2020, with the aim of bringing together council and voluntary adoption agency expertise and resources, to help speed up matching between children awaiting adoption and prospective adopters.
But an evaluation of regional adoption agencies, the first of which went live last year, has found a lack of commitment among councils taking part.
"RAAs were experiencing ongoing challenges around securing buy-in and consensus from participating local authorities," states the evaluation, which involved interviews with those involved in RAAs.
This lack of "buy-in" is among councillors, managers and practitioners and in particular where council-run adoption services are already deemed to be performing well.
"They wondered what they stood to gain terms of performance, sharing good practice or financial efficiencies," the evaluation adds.
RAAs are also struggling to attract staff, including heads of service, with the distances involved when travelling across the region cited as a challenge.
"There were reports of staff anxieties about losing or changing the identity of their local adoption service, and what the new service and culture would look like, and there was an expectation that this would take 12 to 18 months to establish," adds the report.
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Some of those interviewed for the evaluation are confident the arrangement will be more cost effective, although others have concerns it is costing more, particularly around set-up costs.
"There was a common view that the overall set-up costs were high. Some local authorities reported that they were now contributing proportionately more than they were spending on adoption and unpicking the costs to get to this point had been extremely difficult," states the report.
Other challenges include developing shared IT and other back office functions as well as making agreements around staff pay and conditions.
Joint commissioning arrangements are also proving difficult to put in place and some of those involved in RAAs are worried that the link between adoption services and other children's services would be broken.
Despite concerns, the evaluation found that RAAs are starting to improve a number of aspects of the adoption process. This includes speed of matching, adopter recruitment and adopter support.
"There were several reported examples of combining adoption panels leading to more timely adoption decisions," states the evaluation.
The evaluation stresses that this is an early snapshot of a new way of organising adoption services and is optimistic that those participating in RAAs are gradually addressing concerns.
During the evaluation, 10 RAAs were live, while three more are due launch this autumn and the remaining RAAs over the next two years.
"It (the evaluation) paints a picture of frustration and challenge in the early stages of implementation, but also of hope as some RAAs have worked through the difficulties and have seen the first signs of greater collaboration, consistency and improved practice and associated benefits," adds the evaluation.