I had DS tested at 4 years, 3 months. I told him he was going to play with a teacher who had a lot of fun games, and who was very excited to meet him. I told him they were going to have a lot of fun together. He did get nervous when we got there (at that time he didn't always like walking into new buildings/spaces), but the administrator was able to quickly calm him down and asked him things like favorite color, toy, etc.

Good luck!