Went wonderfully! Here's a pic of my lil' preschooler as we were heading out:

His backpack says, "Mr. Strong" a nickname Mark had for him when he was a newborn. Doesn't he look so grown up?!
Here's how it went.............
Harper and I took him to school. I put Harper in the Ergo and walked him in. We put away his things in his cubby which had already been labeled with his name. I put his nametag on and was excited to see it all ready for him too (pinned to the back of his shirt to help university students with names--the preschool program is my alma mater's lab school where students observe/assist, etc.). We made a quick trip to the potty and after washing up, he immediately sat down and started playing with some blocks. There were only a few kids there at that time, but the teacher announced to everyone, "Let's meet our new friend pierce!". I told P I'd be right back and went to the office to get his bike helmet labeled with his name for outside play. I came back and told him goodbye, how much I loved him, and to be good for his teacher. He dismissed me quickly as I kissed his head. As I was walking out the door, I wanted to run back to him and squeeze him tight and tell him again how much I loved him. But rather than make it hard or confusing for him by delaying my exit, I just said "Pssssst P" to get his attention. He looked up. I signed, "I love you" and mouthed it. He returned the gesture and went about playing. Before leaving, Harper and I slipped into the observation booth (we could see him but he couldn't see us). Pierce and a lil' girl (it was also her very first day) were playing on a rocking boat. He said, "This is a boat." She said, "I know".
Harper and I left and came home. It was very quiet at home without him. Even Harper wasn't quite sure what to think of it. Soon enough though it was time to go pick him up. When we got there they were headed outside to play. P's been looking fwd to riding bikes at school for months. As soon as he saw me, he said "I want to go outside". No hello, nothing, just "I want to go outside". I heard several kids address him by name and one even said, "Your mommy's here." Harper and I waited for him to play outside (there were so many things for him to choose from, it was quite funny watching him run back and forth from bikes, sandboxes, playground equipment, water tables, etc. ). After washing up from outdoor play, we headed home. P told me all about his new friends and playing with trains, books, and blocks. When we got home as I was getting him out of his seat, he said, "I want to go back to school Mom!"
It was a big success! Believe or not, I even held myself together, despite breaking down inside (I knew he'd love it and didn't want to give him the wrong impression by being emotional). It's just such a bittersweet milestone!