In England, for example, many early years settings and schools are instructed to ability group their children for phonics whether or not the teachers prefer it - and whether or not the guidance underpinning a specific phonics programme suggests it as part of the rationale.
The blog posting below is a good starting point for launching a thread on ability grouping - it's not about phonics or early literacy - but about the lack of evidence supporting ability grouping - and, importantly, the scenario where teachers may feel they have no choice but to be seen to provide teaching in ability grouping.
The blog is called 'EduResearch Matters' and it is Australian based but relevant everywhere:
http://www.aare.edu.au/blog/?p=502
Novice teachers challenged by ability grouping contrary to evidence
July 27, 2014
By Matthew Clarke
In Australia across most school systems there is no informed, explicit and coherent policy approach to ability grouping. There is in fact a federal and state government policy silence in relation to the issue.
That has not stopped systems, schools and teachers from grouping students according to their perceived ability. The unintentional, ‘ unsanctioned’ or ‘ unconscious’ growth of ability grouping practices in Australian education raises questions of the relationship between policy and practice. Specifically, we usually think of policy as something that leads to practice. But as far as ability grouping is concerned the burgeoning practice across Australia has in effect become policy by default.