At the same time as Audit Scotland, the spending watchdog, is demanding the removal of spare capacity, authorities are being faced with demands to improve buildings and increase provision for special educational needs.
"Those expenditure needs cannot all be met within the current financial constraints," Cosla warns.
It also raises other factors. Shifts in population can separate schools - some dating to the 19th century - from their communities. "It becomes impossible to justify the retention of all schools on their current sites no matter the changes in population over the years and no matter the appropriateness or otherwise of these sites."
Placing requests can also distort a rural catchment area, Cosla argues. "A school roll can be full while the school does not fulfil a local role in that many of its children are not truly local."