When is a surplus an acceptable amount, asks report
But it also predicts that unless the Assembly government takes the lead in tackling falling pupil rolls, Wales could be left "without the right number of educational facilities in the right places".
Councils are coming under increasing pressure to come up with a solution to falling pupil rolls, especially at English-language schools.
But in the document Let Government Commence: The political and service challenges of the Assembly Third Term, the Assembly government is attacked for a lack of support. It is not yet known how the new coalition government will deal with school closures. Labour favours tackling surpluses with closures and mergers, but Plaid Cymru would rather keep them open.
Leading academic Professor David Reynolds, from Plymouth university, also agreed there was a worrying lack of research in Wales into surplus places especially as falling pupil rolls were 13 to 14 per cent higher than predictions in England.
Speaking this week, he said: "We need more central intervention to tackle this problem."
The document says there is also insufficient flexibility on surplus places. It hints that LAs would like to look at other options but are prevented by legal barriers. Likely future investment in school buildings should also be linked with the planning of school places.
But the suggestion that leaving plans to individual LAs could backfire is no comfort to teaching staff, pupils and parents hit by closure plans.
The WLGA's own figures suggest that by 2010 there will be 46,000 fewer pupils in the school system in Wales. In 2006, there were 6,466 less than 2005. This means less money for schools which are paid for every pupil. In Wales, this is around pound;1,500 at primary and pound;2,600 at secondary.
The document makes it clear that closing schools can be costly, taking up to five years. Instead, the WLGA swould like to remove the legal barriers to cluster and federated schools, particularly in rural areas. The Association is particularly critical of AMs who rush to back parental-led campaigns.
An Assembly government spokesperson said: "Two forms of federation have been identified by legislation. The first involves the closure of a number of schools to create a single school on a number of sites. This requires statutory procedures so that interested parties can be involved in the process.
"The second means schools share a governing body but retain separate dentities. Regulations to permit this in Wales should be consulted on shortly."