The last few decades have seen a huge rise in testing and performance monitoring within the English education system. The latest installment is a call for testing of four year olds when they enter the school system. The objectives of such policies are fine enough - this one, for example, will supposedly allow teaching to be more tailored to students needs. There are, however, two big problems with testing in schools. In short these are that: (i) Tests are often poor measures of what is being assessed. (ii) Tests change incentives. Let me elaborate on each of these problems in turn.
How can you measure ability? Exams and tests provide a simple to administer measure. They provide, however, a very, very noisy measure - in other words they often give the wrong impression. And the earlier one does testing the more noisy it is surely going to be because children naturally develop at different speeds. The fact, though, that tests can be wrong is not, in itself, a problem. The problem is that we are biased towards underestimating how wrong tests can be. In particular, the law of small numbers and confirmatory bias kick in and mislead.
The law of small numbers says that we tend to infer a lot from a little. So, if we see Sarah doing badly in a test and John doing well we infer too extreme a difference in their relative ability. Confirmatory bias then means that we tend to see events as confirming our initial beliefs. Basically, Sarah would get a lower mark than John, for subsequent work, even if they write exactly the same thing, because John gets the benefit of the doubt when Sarah does not. As a lecturer I have learnt over the years the power of the law of small numbers and confirmatory bias - and it can be very powerful indeed. That is why I prefer anonymous marking and always try to mark work without reading who wrote it. ('Good' students, notice, have an incentive to make sure I do see their name!)
Given the power of the law of small numbers and confirmatory bias we should avoid noisy measures of ability. That, for me, suggests we should avoid tests that are not absolutely necessary. Or, at least, if we are going to have tests we should view them more as formative and part of the learning process, rather than important measures of ability. Otherwise, we are in danger of children being labelled into self-fulfilling prophecies of success and failure as a result of some meaningless test.
All of this is compounded by the fact that tests change incentives. The more importance we place on tests the more incentive the child, parent and teacher has in getting a 'good' mark. This is obvious - but all too often overlooked. One only has to go to the average school and listen to the parents talking at pick up time to realize how competitive parents can be. Parents, understandably, want their child to be best. And that clearly means they will happily coach their child for a test. Indeed, given the law of small numbers and confirmatory bias this is exactly what a parent should be doing! This is one reason that tests are highly noisy measures of ability.
To criticize testing is easy enough. But are there alternatives? Measuring ability and performance is crucial. The current trend, however, is towards tests and performance measures that give 'simple numbers' that can easily be put in charts, league tables and the like. Such convenience is misleading because ability and performance are not easily measured and compared. More nuanced and rounded measures are, therefore, to be preferred. Teachers clearly do form an overall picture of a student. The schools inspectorate Ofsted forms an overall assessment of a school. These kinds of measures have far more chance of being closer to the truth.