My parents didn't accompany me on my first day at middle school. I was 8yo. School was 1 mile away. I called for a friend who lived nearby and her dad dropped us off in his VW Beetle (the original kind). He didn't get out of the car, just pulled over at the curb.
It was only when I saw parents on the playground clutching their DC that I wanted my DM to drop me off. She could have, but didn't feel it necessary.
Secretly I wish she had.
DS1 has Aspergers, and sticking him on a bus into the unknown when he was 11 was so massive, I couldn't even think about it...I just did it.
He later told me he was very scared, as he didn't know where the bus was going. It was a 13 mile journey, through villages, winding roads and also a duel carriage way on a double decker bus with no seatbelts. How the hell I ever let my PFB board that bus, I'll never know. 
I cried when he took DS2 to the bus stop yesterday. I took a photo of them as they walked away without them knowing.....a big serious one steadily striding off on his regular morning routine, and an excited little one almost skipping by his side, fueled by the excitement of his first day at high school.
I almost felt like I shouldn't take the photo....as if I were invading their personal foray.....