Mike Russell, the party's education spokesman, said composites were often necessary in small rural schools, where it is preferable to save a school rather than insist on separate classes, but there was no need for them in larger schools if the staffing complement and accommodation was up to standard.
He raised the issue with ministers after complaints from parents. Nicol Stephen, Deputy Education Minister, told Mr Russell in a parliamentary answer that composites were "a traditional feature".
The SNP spokesman replied that the Executive had virtually abandoned any attempt to improve standards by decreasing class sizes. "With around 300 composite classes in primary schools in North Lanarkshire, and almost 400 in Glasgow, clearly no progress is being made in trying to reduce the difficulties these classes cause, particularly for children who need substantial help from a class teacher and support from fellow pupils," he said.
"It is particularly concerning that Dundee is the only authority in Scotland which has no multi-composite classes - that is classes of more than two primary stages. This contrasts with 132 such classes in Aberdeenshire and that cannot be solely because of the number of rural schools there."
He added: "The Executive should be improving Scottish education by reducing class sizes and by so doing, reducing composite classes. They seem to be doing the opposite."