The long and short of it is that the pledge of allegiance is exactly what it says on the tin; you are pledging that your loyalty is to the flag (by proxy, to the United States). However, as a US citizen, one has a 1st amendment right that is supposed to protect you from being forced by the government to say the pledge (otherwise known as compelled speech). Constitutionally, you cannot be arrested or otherwise punished for not saying the pledge, or for expressing distaste for the pledge, leaving out the "under God" part while reciting the pledge, or even saying that you think the flag is nothing more than a nationalist propaganda symbol.

That all said, I feel like there is at least one or two stories a year where a student is accosted by a teacher because they refused to recite the pledge. Any teacher who does this is setting themselves and the school up for a lawsuit, as accosting/punishing a student for not reciting the pledge is flat out unconstitutional..

On a different note, as an American who grew up mindlessly citing the pledge throughout my K-12 years, it was a pretty harsh realization when I learned that this is essentially a kind of indoctrination. I honestly feel a bit gross when I go to my kid's school events and the first thing they do is trot out the flag and start the pledge. I wouldn't be surprised if there was a push to have it removed as a regular thing at public schools in the US (nor would I be surprised at a reactionary response from the "patriots" in our country if there was a movement against the pledge...).