I work at Arts&Ideas Sudbury School in Baltimore, 8 years old at this point. I have been with them for two years.
There is no veto. There is simply discussing the issue and revisiting it if necessary. While it is always possible that a disastrous decision will be made, anecdotally, it seems to be exceedingly rare.
Students want the school to succeed. They want to be safe and respected. When you start from those places, bad decisions rarely happen if someone points out why they are bad. Of course, like any group, we may all think a decision is good when, in fact, it is bad. But if someone has a good view or argument, everyone listens.
I have learned that democracy is not about voting. True democracy is listening and being heard. It is a bit like in Buddhism and how simply witnessing and acknowledging emotions will often lead the way to a good outcome.
The absolute core of the school is accepting, without question, that each student is responsible for themselves. Once everyone really gets that, bad intentions melt away.
It is important to have a strong environment for students to experience mutual respect. Starting a Sudbury School is very difficult. But once it starts, as long as a small percentage of new students is added at a time, they will acclimate to the environment and accept the idea of balancing the needs of the many with the needs of the one which is ultimately the balancing act that we all must struggle with.
On many occasions, students have come to School Meeting with a rule that staff did not like. Sometimes during the discussion the staff have their minds changed. Other times, the student might change their mind. Still other times, the rule gets passed and the staff come to see that it is a perfectly good rule.
We also have a jury-style system (Judicial Committee) for rules. It is a body that the staff turn over the responsibility of adjudicating rule breaking and sentence making to. When some students make a mess (no cure for that, I am afraid) and I feel angry, I go and write them up. My anger passes and by the next day, I am okay with whatever our JC comes up with. It is generally fair and equitable.
Students almost always plead guilty if they did it, but if they did not do it, they will certainly say so. And we all get to suggest a sentence, but the members of JC decide on what it will be. They debate thoughtfully and generally rule wisely.
I have seen plaintiffs ask to drop a case while defendants ask to keep it. They want to admit to wrong doing and move past it. There is no shame, just lessons to be learned.
It is the most humane and fun environment I have ever been in. Students learn how to be part of a community, how to accept responsibility for themselves, and how to learn.
They may or may not learn academics; it is their choice. Academics, it turns out, is rather easy to acquire for children coming from a place of empowerment and respect.
To grow up accepted is a powerful foundation to accomplish anything.