I have a 'beginner' student. In fact, my 'beginner' has a handful of English words, has previously worked with self-study materials, and, as a Spanish speaker, effectively knows the English alphabet, and finds many English words familiar. (This is a mixed blessing, as the Spanish actual doesn't mean actual, and you can't call a spade an espada... etc!)
There are plenty of other English learners whose languages have completely different roots, and whose systems of writing don't function, or look, like alphabets. In any country, you might expect most classes to be monolingual, whether the students are adults or children. For the teacher, this has advantages and disadvantages when it comes to speaking and listening, but has to be a plus when it comes to teaching reading and writing skills. At least it gives you a common starting point, even if it's how to hold a pen, rather than a brush!
Where do you start in a school where 30 different races speak 28 different languages?
Where you have 'so many different languages being spoken, some children may be the sole speakers of their language'? Good grief!
I am full of admiration for the staff of Drove primary school, who have developed a programme to work with the realities of a transitory immigrant population. We hear plenty about what happens where integration fails. Someone has taken a good look at the needs of a neighborhood where 'Pupils come and go as their families move to Britain, then in and out of the area as they get established in the country', and done some serious work on meeting the essential educational and social needs of a generation. Bravo.