Familiar... or not?

I went back to my old high school this week with a slight apprehension. I was going there to return some things and to pick up my yearbook. I pulled into the parking lot in the early afternoon. The thing about LCS is that it’s quite a small school. My graduating class was a grand total of 43, and I had known all of them, most of them I had known since elementary school. Not only had I known my own class very well, I was also very well acquainted with almost everyone in the high school. Because of this, going in and leaving without being noticed was quite impossible.
However, I had arrived in the middle of a class period, so the halls were mainly abandoned except for a straggling junior higher or wandering senior who was in no hurry to get back to class. The last time I had been in this building the halls had been filled with familiar faces and the excitement of summer. Now the halls were marked with the sure signs that school was in session: posters promoting different colleges and academic programs, the signs on lockers of athletes encouraging them to win the game on Friday, and the floor strewn with various homework assignments and worksheets.
Basically, nothing had visibly changed. The classrooms were filled with students who I was familiar with but were now older than I had remembered and teachers who I had been under. The front office still had the same smiling secretaries I had passed by everyday. Nothing had changed. Or had it?
The bell rang and students filled the hallway in the same way students had done thousands of times before. This time, though, I noticed so many new faces. The teachers who came out of their classrooms to monitor the passing period were different. There were some familiar ones, but some I had never known before. I was like an alternate reality. Things were so familiar, yet everything was different. It’s shell remained the same, but it was altered enough to make it completely alien. Even though the building was exactly how I had remembered it, it had changed into a place that my classmates and I would no longer recognize.