But education and lifelong learning minister Jane Davidson was criticised this week over how the government's 30-pupil limit is affecting mixed-age teaching.
Janet Ryder, Plaid Cymru spokeswoman, told the Assembly's education committee: "In some schools one year has to be split to meet the 30 in a class. Does this make parents question why their children haven't been allowed to move with their peers?"
But Ms Davidson said this gave "brighter" children a chance to shine earlier. "Estyn (the inspection agency) has said there is no problem with mixed-age pupils, nor evidence that class size makes a difference with older children, but there is a real difference with younger ones."
Statistics show a slight increase in the number of children in mixed key-stage groups, although average class sizes have fallen. Overall, there were 4,791 primary pupils in classes of 30-plus - down from 21,506 in September 2003.