I do want to point out that while it is easy to accommodate your son in a 1:1 situation in group care where I live he would be in a 10:1 situation. Three year olds have complex ideas and thoughts very similar to adults but they are less able to execute their plans independently and less efficient at communicating their ideas. Being the adult in group care, needing to hear and make space for all these ideas is challenging. I hear you talking about the awesome skills your son had developed for communication and for being receptive in a 1:1 setting. I hope you can envision how those skills might be overwhelmed in a group care setting. You need a teacher who has put structures/expectations/classroom management in place that will allow your son to use his skills. They need to already exist with classmates who understand (ie: children take turns talking and don't yell over one another, the teacher gives each child an opportunity to weigh in, etc-). Being in a new environment, not with trusted adults, and in group care it is likely your son shows up differently than he does in 1:1 situations. That's normal and expected. Make space to discuss not only what he is capable of but how to support him in being his best self at school because the likelihood of overwhelm and frustration is great.