Muon, doesn't the standardisation of education serve to reduce the effects of family background on educational attainment, which is essentially the aim of the left? It is clear that the veritable patchwork of schooling choices produced by educational liberalisation is much easier exploited by upper middle-class families; and so serve to make the issue worse.
Not that I'm delighted with the idea of National Curriculums, because that comes with league tables and standardised testing and all associated silliness.
Standardization doesn't help if communities have high levels of learners that lack support on the home front due to parents or their income. The teaching skills needed are different in those communities. Note, I'm not saying that we can't and shouldn't have common minimum standards for outcomes. I am saying that the skill set of the teachers should be matched to the needs of the students to best reach those minimum standards.
I think I'm catching your drift, although I'm curious about what you're leading to. Low-income families have an observable difference in attainment than high-income families; even if schools are funded the same. Therefore, some kind of mechanism is required to further equality of outcome. Your post (although not your partisan affiliation) would imply that low-income schools need a "subsidy" (for lack of a better word) to attract better, well-paid teachers than high-income schools (which already are effectively being subsidised by the already discussed effect of high income parents).
I'm not sure that voucher schemes (and the like) are an effective way to "subsidise" low-income areas (based on my British experience with the "free school" experiment) but I'd be happy to be proven wrong.