The teacher uses their experience to assess the skills of the child, asking the child to read aloud is a good test, observing if the child points for example instead of answering.
The OP was talking about children born and raised in an English speaking country. He mentioned children being unable to speak in either language. I find that hard to believe. Children learn to speak, in any normal distribution there will be some who cannot speak or opt not to speak, this is a tiny minority.
What is being measured is active and passive skills this has to be by teacher assessment because of the age of the child a formal or quantifiable test is not appropriate. Formal testing happens later at around age 7.
At each stage the teachers concerns if any are noted and assessed to see if additional help in needed. There is a wide range of help available, children who don’t speak are moved to special schools. Parents sometimes move their child to another school but the paperwork goes with the child.
Children are not allowed to languish unaided ie passed from one class to another this simply doesn’t happen. What we are talking about here is the professional ability of the teacher and the structural nature of the school. If a child doesn’t acquire language questions are asked of the teacher and school
Acquiring language is not a formal, grammar rules based thing almost all children speak irrespective of the language or languages of the parents.
The OP also talks about sets or streaming by ability, though starting to make a comeback, streaming has not been widely used in Primary schools for about 20 years.
From reading the opening paragraph I know the OP is not involved in either education or child development.
The advice given by the OP for parental engagement in their children’s education is grand we all know this and it can’t be stressed enough.
A number of glaringly obvious errors in practice and an extremely outdated view of education shine through the advice. It’s a rather conservative and incorrect view of education wrapped up in an attempt to portray Polish kids as somehow backward and Polish parents as unengaged with their children. The questions I would be asking are why is it that a teacher is unable to teach all ability pupils? and Why blame the kids/parents?
The king in his castle and the pauper at the gate and so shall it remain is how many see education, reinforcing their own prejudices that’s why I pointed out that teachers have to talk down middleclass parents and talk up working class parents.
Hey! So how do you really say wywiadówka in English?
Parents meeting, the time is irrelevant.
From what Concerned described on the UK scene, one migth presume that the Polish kids there interact mainly with their own kind in Polish, broken English or a hybrid thereof. Is that indeed the case?
No this is not true,Polish kids born in the UK speak English.
This is strictly impressionistic
And contradicts the OP
I'd like to add that according to threads I've read here about raising a biligual child (if I remember correctly) it's normal for a child to slow down in progress of acquiring speaking skills. It doesn't mean that later those kids won't catch up.
All children develop at their own speed there is nothing abnormal about very young children taking their time.
There is something that needs to be said here, all children are individuals all develop at different rates.
Hit the button early by mistake