Conditional past-future

optilang: «I would go/be going home earlier - I have not yet gone home (I still have some lessons to teach)»

It doesn't matter when you will go home. The only important detail is the time of your hypothetical going home. If it's prior to the moment of speech, your choice is the Type 3 conditional ("would have"), and the mixed conditional (just "would') otherwise.

EDIT: optilang: «The absent student was not the last one of the day - and if I had known that he wasn't attending I could have moved a later class to his slot - resulting in me being able to leave earlier. »

1. (moment of speech — 13:00) If I had known you would not come to the lesson I would have gone home at 12:30
2. (moment of speech — 12:00) If I had known you would not come to the lesson I would (could/be able to) go home at 12:30

That's right.

 I would love to see some examples if you have time to share them

Thanks 

 

optilang

To me  to you would have seems better than using would even for the future.

It seems so.  To some ears it is preferable to relax the logic of time rather than change a well established grammatical structure (If ... had ..., ... would have ...).  I think my ear is similar in this respect.  I would recast the sentence as one of these:

If I had known that he was going to cancel, I could have gone home early. 

If I had known that he was going to cancel, I could have arranged to go home early.

If I had known that he was going to cancel, I would have arranged to go home early.

____

I don't think I would use:

If I had known that he was going to cancel, I would have gone home early.

That seems to indicate that the time has already passed to take the opportunity to go home early, which is not the case in your example.  The same sentence with could doesn't have this objection to quite the same extent, so I put it in the first group, even though it may be considered a borderline case.

CJ