I liken comments to a yo yo.............
week one - 'Thanks for this - Johnny thoroughly enjoyed reading this book AGAIN'
week 2 - (book way too hard clearly by way of punishment for daring to point out that teacher hasn't noticed child's had book before)'think some of the metaphors were a bit lost on him' given War & Peace type novel
week 3 - back to Janet & John...
and so it goes on.
I think it's all a bit of a power trip by the teacher. Best to just smile, say something nice and bland, whatever the apprpriacy of the book & child's understanding/ not, and let them read their own stuff.