Thank you! затем is also a compound word. It is made out of за, in this case meaning ‘behind’ or maybe ‘at’, with the instrumental case of что (чем – meaning ‘with what’). отчего, on the other hand, is composed out of от, i.e. ‘from’, and чего, the genitive case of что (meaning ‘of what’).
I'll just put a couple of notes here for any non-native English speakers reading this:
"Why are they not in the school?" / "Why aren't they in the school?" To me this suggests they might be, for example, outside the school playing. By contrast, "Why aren't they at school?" suggests they're not even anywhere near the school property.
"Why are they not in school?" To be "in school" in English means that one is enrolled as a student and actively attending. "She is in school" is like "she is employed" - it doesn't necessarily mean the student is at the school right now. There's a post further down on this page that explains the Russian equivalent.
keinemeinung wrote: You could say "Они ходят в школу?" (are they going to school?) or "Они учатся в школе?" (Are they studying in school?)
JustLearnen has a point (though we can assume he/she means 'physically' and not 'psychically'). nDroae notes are somewhat misleading.
Usage of IN and AT varies depending on an English speaker's type of English (American vs non-American generally) while using THE highlights/focuses on the particular physical space or location.
Kids are AT/IN school on weekdays while parents are often AT THE school in the afternoons to collect their kids (from school).
'I have to collect the kids at school?' OR
'I have to be at the school by 4 o' clock to collect the kids?'
If you are AT THE school, you are on its GROUNDS/PREMISE, and may or may not be in(side) the school building. If you are IN THE school, you are likely on its PREMISES in(side) its building(s).
Using IN/AT without THE can apply to both being a student and also being at/(in the) school (at a particular moment in time).
Therefore, I am unsure how apt or helpful to learners the 'Russian equivalent' referred to below is.
Yes. It is grammatically incorrect.
You can say:
Why are they not in (the) school?
Or use a contraction and say:
Why aren't they in (the) school?
Use of 'the' would be unusual because it would be referring specifically to the physical building and not the idea/concept of 'being at/in school'. Parents might be IN/AT THE school to collect their children or there to speak to their child's teacher.
Husband to wife:
(H) Where are they kids?
(W) It is only 1 o'clock, they are still at/in school.
Teacher to students?
(T) Why isn't John at/in school (today)?
(S) He is sick today, Miss. (He's out sick.)
Use of 'IN and AT' varies depending on an English speaker's type of English (generally American vs. non-American). Usage is generally quite interchangeable and based upon preference.
But if you are IN or AT school, it refers to being a student or being at the place where you are learning/studying.
What do you do? I am still in school. Where are you now? At school.
(If you are American, school may also refer to college/university, this is less common usage for non-Americans)
I can hear «в» (pronounced [f] because a voiceless consonant follows) pretty well.
On occasion--but not in this sentence, where I hear it just fine--I have caught the TTS omitting в completely on the slow speed when it is the first word in the sentence. If you come across that and agree it's problematic it might help for a native speaker to report it as well as us non-natives. :-)
«Почему́» is 'why?'
The mean meaning of «чего́» is 'of what?'. It can mean 'why?' in colloquial Russian, but this is non-standard usage and Duolingo probably won’t accept it.