How will differing ages be taken into account?

The PIPS and iPIPS assessments are able to be conducted with children from age four to seven years.  We have published data showing that it is quite possible to control for age and still be able to measure attainment on a meaningful basis.  There are more or less linear relationships in children's attainment in early maths, reading and vocabulary development for this age range across the sample of countries available to us.  This allows us to make valid comparisons between children of different ages.
The chart below shows the early mathematics scores of children aged four to just over six years starting school in England, Scotland, New Zealand and in two states/territories in Australia.  The y-axis shows the age rising on three month intervals from just four years to six years and three months.  There is a clear trend between age and development and clear differences between jurisdictions.