As a parent I agree with RollonSummer - this measure in relation to merely one child in a school (regardless of disability/ family circumstances/ illness) failing to pass the proposed maths test is Draconian and will only pressure staff & pupils.
Far better to use the budget for this new magic maths test in a targeted way for improved resources/ training/ equipment to support mathematics at schools which are failing >10% of pupils (6% being 2 out of 3 pupils).
Start with the obviously troubled schools where say for example 50% or more pupils fail to achieve NC L4 in maths and then move on from there.
Of course this would require some form of centralized control of schools - and of course the present coalition has rather destroyed the LEA model of local control of education with their academies schemes.
Philosophically the present government prefers to view education as an expensive service which is best 'outsourced' thereby shifting blame for any inadequacies/ problems on 'private companies' (aka academies) and away from local or national government.
Meanwhile they micromanage 'outcomes' by setting targets without specifying how teachers are meant to get their pupils to arrive at such targets (allegedly the bonus of such an approach is this is giving teachers freedom to teach as they/ local area desire) and this government feels the best solution is to set up a guillotine whereby HTs/ Senior Management are removed if targets aren't met. This is of course, regardless, of what this pressure means for morale.
A struggling school may need staff changes - but automatically presuming it's the head's fault seems rather a knee-jerk reaction. Why children fail to achieve NC L4 has been a persistent problem in the UK and one many governments have failed to solve with a wide range of initiatives. Perhaps the solution is to work out what actually works across all schools of varying socio-economic mixes in a community/ region and then roll that policy/ procedure out nation-wide.
At present it isn't a level playing field - some schools are well equipped, have amazing resources, on-line maths homework/ tuition schemes and excellent teaching practice. Other schools are less well provisioned. Throwing money at the problem isn't the solution - but there is a need to level the playing field and maybe schools with persistent low achievement need better resources, better training, more attractive salaries (education loan forgiveness schemes?) for teachers/ after-school support for further tuition for struggling pupils, etc.... to level the playing field for those children. And maybe as a society we need to see that investment (because it will cost money) as an investment for the whole society's greater good.
We've had decades of a persistent low-achieving cohort of ~20% of pupils - so whatever else what has been attempted to date hasn't worked - and the likelihood is another test isn't really going to solve the problem either.