Politicians would love, simply, to say "we spent money and things are better" but to do so they would need to trap children in the "criterion referencing" of past children's performances, so that they could evidence "better standards" or whatever.

This would be an impossible brake on learning. In practice they can only say "we spent money and things are different; here is why different is better" and there is an evidence gap between "better" and "different". The Learnometer project seeks to help bridge that gap....