I think this view is just to generalised, every child (even adults) are affected in some way by exams/tests. Ok - some children will sail through the tests, but a majority of others are quite capable but would/will fail due to bad poor exam technique.
YES - technique not just practice, for example - (quite) a few years ago I started microsoft accreditation, the first exam I failed miserably - not because I didn't have the knowledge - but due to the lack of technique:
=> time - I ran out of time, so speed and accuracy can only be accomplished by practice
=> interpretation - wording of questions can be the downfall in any exam, again analysing of past questions is essential to understanding the content.
=> practice - so are we saying all those past '0' / 'A' level papers I practiced at school was a complete waste of time? I don't think so!
=> Confidence - no confidence = poor performance - more practice and seeing the increasing test results has bound to have a positive effect.
...and after I practiced and improved the above - I passed all the exams.