Your sentence is in 해라체, the lowest formality level whilst 다녀요 is in 해요체, the higher casual level.
다니자 is in 해라체, and 다닙시다 is in 하오체. It is not "off", but it is a matter of different formality levels.
This exercise is in 해요체, in the propositive mood. What could be a better translation in your opinion?
What would be the difference between Let's attend school together." and 'We attend school together.'
Assuming the subject is excluded of course.
Or is that how we know.
In this formality level I don't think there's any way to tell unless you go off context and/or tone of the statement/command
This usage of 요 as "Lets" is really weird and uncommon. I wonder why this is presented before the other common forms like 자 or 읍시다. It is also very confusing
I presume you don't speak Korean fluently if you think it's weird and uncommon. This skill is about 해요체 where -아요/-어요 makes the propositive mood. This is an open forum where everyone can see and learn from what you write. Please refrain from stating your unconfirmed opinions as a fact.
I speak Korean fluently and I think the use of "let's" is strange...
I thought this was just as common as those two as said by some Korean instructors from another Korean learning website?