There are two problems for the Labour politicians running the Welsh Government. Firstly it is they who made PISA results such an important measure of progress in education and it's they who have been in charge of education here since the Assembly began, even when it was run by coalition governments.
The first is why the First Minister and Education Minister made no attempt to portray the figures as anything other than a disappointment. The second explains why opposition parties joined forces in the Senedd in a rare concerted attack on the First Minister. But watch Westminster closely too.
You'd expect Tory MPs to pin the blame on Labour. But it was Labour's Shadow Education Secretary who said that 'Wales has some difficult questions to answer' and some Welsh Labour MPs are also privately worried. You can be certain that they'll let their Cardiff colleagues know their concerns.