What is really happening in Squeers's "practical mode of teaching"?

‘This is the first class in English spelling and philosophy, Nickleby,’ said Squeers, beckoning Nicholas to stand beside him. ‘We’ll get up a Latin one, and hand that over to you. Now, then, where’s the first boy?’

‘Please, sir, he’s cleaning the back-parlour window,’ said the temporary head of the philosophical class.

‘So he is, to be sure,’ rejoined Squeers. ‘We go upon the practical mode of teaching, Nickleby; the regular education system. C-l-e-a-n, clean, verb active, to make bright, to scour. W-i-n, win, d-e-r, der, winder, a casement. When the boy knows this out of book, he goes and does it. It’s just the same principle as the use of the globes. Where’s the second boy?’

‘Please, sir, he’s weeding the garden,’ replied a small voice.

‘To be sure,’ said Squeers, by no means disconcerted. ‘So he is. B-o-t, bot, t-i-n, tin, bottin, n-e-y, ney, bottinney, noun substantive, a knowledge of plants. When he has learned that bottinney means a knowledge of plants, he goes and knows ‘em. That’s our system, Nickleby: what do you think of it?’

‘It’s very useful one, at any rate,’ answered Nicholas.

‘I believe you,’ rejoined Squeers, not remarking the emphasis of his usher. ‘Third boy, what’s horse?’

‘A beast, sir,’ replied the boy.

‘So it is,’ said Squeers. ‘Ain’t it, Nickleby?’

‘I believe there is no doubt of that, sir,’ answered Nicholas.

‘Of course there isn’t,’ said Squeers. ‘A horse is a quadruped, and quadruped’s Latin for beast, as everybody that’s gone through the grammar knows, or else where’s the use of having grammars at all?’

‘Where, indeed!’ said Nicholas abstractedly.

‘As you’re perfect in that,’ resumed Squeers, turning to the boy, ‘go and look after MY horse, and rub him down well, or I’ll rub you down.’