I would never say forced - it's just normal practice, but abstention happened. Shared experience is a powerful uniting factor. Reinforced daily, even moreso. Every student remembered the Pledge itself and remembers seeing every other student doing it - regardless of race, creed, or color. We were all Americans. I remember the first times I saw someone not taking part, the first, it was for religious reasons; his parents were part of a religious group that wouldn't let them swear oaths or something like that. The second was much later, and it was how I found out that someone in my class was a resident alien.
It's obviously a stand-in for a religious prayer; I don't think anyone past 4th grade had any misconception about that. It's also a prayer of nationalism and loyalty to the country. If we could bring people back together like that still, it would help.