All boys will attend roll-call at 8 o’clock.
Above sentence is from a Korean dictionary, which says it can denote order or instruction. It’s not common to use the meaning when the subject is the third person, it says. Then if the subject is replaced by ‘she,’ can’t this sentence take the sense of order or instruction at all: ‘she will attend roll-call at 8 o’clock’?
I think when you say:
All boys attend roll-call at 8 o’clock.
you are stating a scheduled occurrence, that's all.
But when you say:
All boys will attend roll-call at 8 o’clock.
it seems that there was some order, expectation or requirement that this will happen. If spoken, the word will might be emphasized.
Same would apply to:
She attends roll-call at 8 o’clock.
and
She will attend roll-call at 8 o’clock.
