Below is part of an essay on lesson planning from the frenchteacher.net website. One thing I would add to it is that these days Ofsted inspectors like to see evidence of progress within a lesson. This is problematic in languages where we are gradually accumulating skills over a long period. If you neglect good models of target language I think it is inevitable that pupils' listening skills and general comprehension will be poorer in the long run. Therefore you should judge progress over months and years, not 60 minutes.
Here is what I have written. I hope it represents common sense for young teachers setting out on a language teaching career.
"Language teachers talk a lot about this and it is fair to say that
opinions vary! I’ll put this as simply as I can: children need to hear
lots of the target language (what is sometimes called in the
jargon ”comprehensible input”) to allow their brains to exploit their
natural language learning capability. But children also need to develop a
relationship with you, the teacher, and they need to understand what
they have to do in a lesson.
So, my rule would be use the target
language most of the time, maybe in chunks of ten minutes or so, then
“release tension” with some English. Try not to constantly “echo”, by
which I mean use a bit of French then instantly translate it into
English. Why should a child bother to listen to the French if they know
you are going to translate it? Remember that we tend to over-estimate
how much a child understands in the target language.
Why not occasionally check meaning with a Comment dit-on en anglais?
Whatever you do, don’t lose the class by speaking too much of the
target language for them. Students often report that that they lose
interest when the teacher doesn’t use English enough. Match your use of
target language to the needs of the class, but try to use as much target
language as you can. Don’t get lazy about it.
Ultimately the amount of the target language used will depend on the
quality of the lesson planning. A well-planned lesson with good visual
support will allow you to use lots of the target language with nearly
every class. Use mime, gesture, cognates, flashcards, pictures, powerpoint,
written words on the board – whatever it takes."