In an earlier opposite translation i wrote a school and it was marked wrong as the school. Here you have chosen a school. How can the gaidhlig to english translation insist and mark as incorrect the same translation then?
are you sure it didn't say "anns an sgoil"? That would be "in the school".
This would have been a good place to use a specific day instead of a-màireach. There are many such opportunities in the lessons that follow the days of the week section, but they are not being used.
I was marked wrong though I wrote that . Can it be because I didn't leave a space between a' and teasgag? That's the only mistake I can see.