No it is no a slang , it is not that informal.
This is a very tricky one but your asking I’m tall when I’m young, and I’m short when I’m old, I first thought about a sponge but it’s a candle.
Dicken's object of social criticism which is referred in this excerpt is that, the system of education which treats children as if they are machines. It is shown in the novel that only the society but it did not focus on its emotional context.
Teachers only cared about the results of the input which they gave and if is not corrected then the students will bring to the society.
This is the reason why there is a big gap which is between the poor and the rich. Rich believes that the poor can make it if they can strive harder.
