Past tense. "when Tom went [was going, would go, used to go] to high school."?

Question

I'm confused with how to mention past habits.

If Tom is a student now, you say "Tom goes to high school", right?

If Tom already graduated, are these three all OK?

• A-1) Tom went to high school until last year.
• A-2) Tom would go to high school until last year.
• A-3) Tom used to go to high school until last year.

I doubt "Tom was going to high school until last year." is a correct sentence. Is my understanding correct?

How about the sentences below?

B) Tom was dating Becky when he

• B-1) went to high school.
• B-2) would go to high school.
• B-3) used to go to high school.
• B-4) was going to high school.

Which sentence would be most appropriate? Tenses are the most difficult part of English to me.

Answer 1

For the first one A, the first and third ones are correct

Tom would go to high school until last year.

^ is technically correct but the sentence does not flow well in a way

It is more grammatically correct in one writes

Tom would go to school last year.

I doubt "Tom was going to high school until last year." is a correct sentence. Is my understanding correct?

^ This sentence might be correct, I think its grammatically correct, but it sounds weird, so its better to stick with the other ones you have mentioned.

For B, all 4 correct, as they all imply how Tom dated Becky using past tense.

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For the comment on the following:

But I still do not understand why "would go to school until last year" is weird while "would go to school last year" is OK. Would you explain what makes this difference, please?

To be honest, both these sentences actually have different meanings, "would go to school until last year", implies that Tom stopped going to school at the start of last year, and "would go to school last year", means Tom used to go to school last year and ended school probably at the end of the year.

E.g. The current year is 2022, put the first sentence into perspective (would go to school until last year), then it means Tom stopped going to school at the start of 2021. To clarify, "until" means "up to", so Tom stopped going to school when 2021 started. The second sentence (would go to school last year), implies that Tom stopped going to school when 2022 started.

Answer 2

Go in go to school is not the same as the normal word go: it is already habitual.

Therefore your A2 and B2 are not idiomatic in this sense. You can say He would go to school ... but this would refer to his daily journey to school, not to the fact or period when he was attending school.

Your A1 is normal. A3 is possible, but implies that something unexpected had happened to make him stop.

In your B, again, B1 is more natural, B3 is possible (with the same implication as A3), and so is B4; but to me the most natural choice is when he was at high school.