Maizie: I wish they'd just put up with a bit of 'unnaturalistic' text for a few months!
They do! The early phonics texts are all excruciatingly boring and repetitive because they strenuously avoid natural language which invariably includes some high frequency words with irregular spellings.
The number of relatively common words which have letters with variable sounds (e.g. an - any, on - only, once) is around 2 000.
The ones which impede reading progress most seriously are the 37 among the 100 most used English words:
he, of, the, to, was, all, be, are, have, one, said, we, you, call, come, could, do, down, into, me, now, only, other, right, she, some, their, there, two, when, want, were, what, where, which, who, your.
And the following in the next 200 most HF:
another, any, many, water, small, laughed, bear, great, head, ready, each, eat, sea, tea, please, eyes, find, friends, giant, I’ll, I’m, key, live, people, pulled, put, thought, through, work, would, coming, everyone, gone, most, mother, oh, once, grow, how, know, snow, town, window, book, food, good, room, school, soon, too, took, door, Mr Mrs
Their irregular spellings ensure that children can't learn to read those (let alone write) with just simple phonic sounding out and blending. That's why they keep being sent home for learning by heart.