Offering 0pen and Honest Professional Advice
Who Wants to be Average? When will the Media Learn we are Unique Human Beings not Clones.
As research into working memory illustrates, the learning potential of children has and will never be equal and learning will always be more difficult for certain learners to achieve than others. In subjects like maths, which make vast demands on working memory, it is possible to predict which children will be able to cope with A'Level Maths at a early age.
The evidence that working memory capacity is dictated by genes. It could be viewed as being like running capacity. There is a Times Educational article that clearly illustrates that children's learning potential can be worked out through referring to their genes. This is unlikely to be an exact science.
We cannot consider children as average. There is no such thing as average person. It appears be a historical anachronism to view Pisa, which is based upon creating a countries estimated average score, as a valid assessment.
The will be more discussed about this this Autumn
See Evidence - Researched Papers and Review of the subject