Stylistic fronting (as opposed to phonetic fronting), also called front-focus, moves elements traditionally placed to the right of the verb, to the front. It’s typical of Icelandic and Scandinavian languages and in Old and Middle English, so it’s nothing new.
I don’t know if and and why schools are concentrating on adverbial fronting, but anything that moves composition on from basic SVO, subject, verb, object is good imo.
People may be familar with the 5Hs and W principle - who, what, where, when, why and how? It’s the basis of fiction, journalism, detection and all manner of topics that need enquiry. Which of the 5Hs and W has primary focus, depends on context and what effect the writer is trying to achieve, what he or she wants the reader to focus on.
Prepositional clause:
A boy stood on the corner waiting for a bus.
Fronted (where):
On the corner, a boy stood waiting for a bus.
… changes the focus from the boy to where he is waiting.
As the story is developed, the writer may chose to say more about the corner. What is on the corner? Is it a house or a shop? Does anyone live there? Is there a garden? Is the shop open or closed? Is it dark? Is there a broken street light? Is the bus stop near the corner? Is it raining? Is he sheltering there temporarily until he sees the bus coming? And so on.
Adverbial clause:
She removed the hot dish from the oven very carefully.
Fronted (how):
Very carefully, she removed the hot dish from the oven.
… changes the focus from the woman removing the dish to how she did it.
Why is she being very careful? Is she old and infirm? Or is she young and inexperienced and her parents are letting her cook dinner for the first time? Is the dish too full and likely to spill? Has she just grabbed a thin tea towel rather than oven gloves so knows she needs to be more careful how she holds the dish?
We’ll go out tomorrow, if I’m free.
Fronted (who):
If I’m free, we’ll got out tomorrow.
… changes the focus from the first person plural to the first person singular.
What’s the relationship here? Is there an imbalance? Why would someone put themselves first in that sentence?
I agree that in amateur hands, fronting can look deliberate and clumsy but in the hands of developing writers it adds drama and feeds the imagination.
What I would be concerned about in a school context is that the exercise is just going through the motions with little or no time to discuss why one might choose to switch the focus. Are children being encouraged to think about why?
When used by skilled writers, it can add drama, imperative, surprise and urgency e.g.:
Shakespeare’s Lear:
Come not between the dragon and his wrath. Or/
Do not come between the dragon and his wrath.
Tolkein’s Hobbit:
Out jumped the goblins. Or/
The goblins jumped out.
Suddenly, up came Gollum and whispered and hissed. Or/
Gollum came up suddenly and whispered and hissed.
Which do you prefer?