The technique that I have observed having the greatest, and quickest, impact on talk/oracy is the use of Pupil Talk Prompts. I have seen this in my own classes, and in schools that I work with.
give confidence to join in
enable more powerful, articulate speech
impact on writing
I recommend having Pupil Talk Prompts on display so that children can see them in every lesson. You might want to put them up gradually, introducing one or two each week.
Having a set to put on tables or place in the centre of a circle will raise their status even more and can be a key resource for specific learning tasks.
Keeping an additional set available for interventions out of class will ensure that all children have consistent access to the prompts.
You are welcome to download my list of Pupil Talk Prompts and use them as you want, for example creating your own set of prompt cards.
I’ve also started selling resource packs of prompt cards - contact me if interested.