"I was not in school yesterday." has an identical meaning and should be accepted.
Whoa........did you guys just introduce the locative case without any explanation whatsoever? Somebody might want to do something about that - even just a quick note at the beginning of the chapter saying it will be briefly used but fully introduced later? It makes it very difficult to find the lexical form of a word if you don't know the declension being used when it's presented.
It has been indicated several times that we had to stop developing Tips nd notes because Duolingo started to make changes to the format without ever settling to some final form. They claimed it will enable mobile users to have the Tips and notes, but that has not happened. So we don't know if the format will stay or not.
We can perhaps do something short you suggest but especially anything involving tables may become unusable in the future.
Ah. I haven't run into any discussion about the tips and notes, and I took a break from studying for awhile and they improved considerably during that time.
Something short and maybe a link to a webpage, or a a link to an online grammar might be helpful. So I guess this is actually where the locative is being introduced.
I find the tips and notes really helpful - I actually even really like it if the tips and notes include a list of new vocabulary for the unit so I can add it to my Anki flashcards and begin to memorize it before even attempting the unit. That's just my personal opinion, however :)