But assessment is a beguiling process. It can, it seems, diagnose pupils' strengths and weaknesses, report on their achievements, judge the effectiveness of teachers and schools, track the performance of the system and enable significant comparisons to be made. What is often overlooked, however, is that it cannot do them all at once.
People respond differently according to their perceptions. If the tests for four- and five-year-olds are seen by parents and teachers as being solely to help the children then they will be happy to let weaknesses show. But if the results are also to be used to classify children, or to attempt to calculate the value added by a school, then a different mind-set will come into play. It is a bit like the difference between a counselling and a selection interview - aiming to get at the truth vs putting the best face forward.
The trouble with the baseline tests, as they have been presented, is that it is not clear what they are for. Their very name suggests that the original intention was to have some scores from which to try to gauge the effectiveness of primary schools. But the launch focused on their diagnostic function.
The Government, however, also apparently envisages that the results will be used to assign children to different sets. Charles Clarke, the new junior minister for schools, was reported as saying that this is something he personally favours. If that is indeed the case - and we cannot be sure, because New Labour has been ambivalent on selection - then it could completely undermine any diagnostic intent.
Imagine what would happen. Ambitious parents would get hold of copies of the tests and try to train their offspring from the cradle on the specific reading, writing and number requirements, so that they could get a flying start to their schooling. A jolly good thing too, you may think, given the extent to which this country seems to lag behind others in literacy and numeracy.
But there is a paradox. Countries that do best in international comparisons, such as Germany, Hungary and Switzerland, start primary schooling later than we do. What these countries have long recognised is that to press ahead with reading, writing and arithmetic too soon is counterproductive. If children are required to take in ideas or make appropriate marks on paper before they are conceptually or physically ready, then their early experience of education will be of failure.
Some may never get a proper foothold or recover their enthusiasm for learning. The success of the top-performing countries seems to be based on an excellent kindergarten system which brings all children to a state of readiness for schooling without forcing the formalities.
Britain's poor showing in literacy and numeracy, the huge spread in performance, and also, incidentally, the gender gap, could all stem from a tendency to try to push literacy and numeracy too hard, too soon. Those who can cope do, but those who can't - predominantly boys, and children from poorer homes - fall further and further behind. Baseline tests used for setting children or judging schools are likely to exacerbate this. It is evident from the results of the Qualification and Curriculum Authority's pilot study, published last week, that girls outperform boys on every part of the tests.
The Government rightly has as its main educational priority getting all children, irrespective of their starting points, to high threshold levels of literacy and numeracy by the end of primary schooling. If its targets for age 11 are met, this will be an important step towards a fairer society. Baseline assessment, by providing better information, can help teachers as they seek to raise all their pupils to the desired levels.
But if the results are also to be used in assigning children and judging teachers and schools, then it will have the opposite effect. The tests will then tend to exaggerate the differences between children. Those from lower socio-economic backgrounds, and boys especially, will be further disadvantaged, increasing the long tail of underachievement and the gender gap. The implied pressure to achieve literacy and numeracy at ever-earlier ages - before many children are ready - will tend to stoke up emotional resistance to learning. and may well depress overall achievement.
The new tests could help or hinder. The Government must decide what their prime purpose is to be, and tell us clearly. Is it to help the teachers, in which case the results should be confidential to them and to parents? Or is it mainly to classify children, or to measure schools? The Government cannot have it all ways.
The writer is the Sydney Jones Professor of Education at the University of LiverpoolReuse content