How teaching assistants help children express themselves?

Answer 1

They break down the complex language barriers that can exist between the teacher and student. Sometimes children cannot express themselves simply due to the fact that they do not understand the expectations of others. This means that the child will revert into it's self or get very frustrated. They communicate with the child at it's particular level, giving the child confidence.

Answer 2

I suppose you mean untrained people who assist class teachers.
If so they can observe and learn that way, or read appropriate literature. Certainly shy kids need encouragement when they try to express themselves - a clap from the class perhaps, and positive, not negative, criticism from the teacher. A child could be asked to share a special interest with the rest of the class, especially if the rest don't know much about it.
I'm sure some "real" teachers will give you better answers.

Answer 3

I wish to make a note to Malcolm, who answered before me, teaching assistants are trained, my friend is studying to be a teacher's aid (or child care assistant).

Anyway, teaching assistants are there to support the teacher when classes get to ridiculous sizes and one person cannot cope with every student.

Teacher's aids make it easier for every student to get attention, which in turn helps the student's express themselves as they feel that they are not forgotten and are important enough to be heard.