You must trust before you can communicate.  So before we continue talking about communication I would like to stop and talk about bonding with children.

We want children to be able to express their anxiety so that when we ask a child to take a risk and try an activity that is going to produce anxiety, that child can trust that the teacher truly cares about the his/her well being.  As teachers, we do not have the right to impose behavioral expectations on a child until we forge a relationship with that child based on trust.
For a typically developing child, raised in an environment with caring adults, a trust of adults and a belief that adults will provide support is part of normal relationship building. But for the child that does not have an understanding of relationships, the normal “I like my teacher and my teacher likes me” may not happen.
A typically developing child goes off to school knowing that pleasing the teacher is going to make his/her life easier and more pleasant. AND even more important, the typically developing child feels safe that if he/she cannot do the work, or is inappropriate, the teacher is STILL going to like him/her. The typically developing child feels that even if he/she gets in trouble, the teacher will find a way to talk to him/her about the problem and probably end the whole affair with a hug.
Children who have not been raised in an environment with caring adults, children who are on the spectrum, or children with emotional disabilities, need help bonding with adults who do care about their wellbeing. And that bonding should be done without expectations.
As teachers, we get caught up with praising children for doing behaviors that we like to see. We inadvertently place expectations on that child and that causes anxiety -which reduces the possibility of socially appropriate communication.
For example, when a child with ADHD walks into the room quietly,  if you say, ‘I like how you walked into the room.” You have praised the child for their behavior.
BUT if you say, when a child with ADHD walks into room, “Gosh I am soooo glad we get to be in the same room together today. ” Now you are bonding. Now you are simply saying I like sharing space with you. No expectations – just sharing space.
For the child on the spectrum who needs structure and clear expectations, a welcoming smile lets them know that they are in a space with someone who is going to help them manage the rest of the day. Someone that they can trust to provide the supports that they need. And that’s a great place to start your day.
Years ago, I was training to be a teacher in front of my instructors. I was working with a 4 year old child stacking blocks. It was a difficult task for her and getting three blocks stacked was just impossible. When the task was over, she climbed on my lap and I gave her a hug. My instructors admonished me for giving her a non-contingent hug. “Wait until she does something right and then hug her.” I probably failed the assignment but I remember saying -"Well she sure does cute right."
I wrote this song in response to their concerns.
https://soundcloud.com/chris-curry-music/terri-1?in=chris-curry-music/sets/sunshine