Unfortunately, I do not believe it is possible to stop genocide. I believe it is, in part, due to emotions that take on a massive scale. Let us not forget Pol Pot killed 25% of his own country's population (2 million out of 8 million) in Cambodia during the 1970s. More recently, the genocide in Rwanda where the Hutu government killed hundreds of thousands of Tutsies, and the still (on again and off again) slaughtering in Darfur, Sudan.
It is a byproduct of hate and education is only a small influence in a person's (or nation's, or society's), attitudes. Hate is learned from many different sources.
The United States actually has a fairly good educational system, but you still see members of the Ku Klux Klan spout their racial and ethnic hatreds. Education didn't do them any good at all.
Teaching our children to be open-minded and tolerant people is effective on an individual basis and it certainly helps. I have taught my own, now adult, childred those values. But if my family had been slaughtered for no other reason than their identity with an ethnic group, I don't think I would be able to teach any children I had left to be tolerant of the offending group. I don't think very many people around the would are modern-day Gandhis. Thus the cycle of hatred remains unbroken.
I think the best way to stop such genocides is world-wide condemnation and direct, effective action taken against the offending government. We have not done that.
Vigilance, and education. We can prevent genocide by making sure our children know all about it. We can prevent it by never letting it go unanswered or unpunished. We can raise our children to be tolerant individuals, willing to accept others for what they are, whatever they are.
The one lesson I try to really push when teaching "What does the Holocaust mean for me" is looking at it not from the perspective of the perpetrators nor the victims, but what about the millions of people caught in the 'middle' who did nothing? How many kids in school today consider themselves innocent if they are not being the bullies nor being bullied. I think those in the middle, turning the blind eye to the bullying, are just as guilty as the bullies themselves.
There was a time I would have said that as a result of the publicity of what Hitler did in WW2, genocide could never happen like this again. But it could, if enough people ignored the signs at the very beginning.
One thing is to teach tolerance and to try to make people see the fundamental similarities between them so that they will not want to kill one another. This is difficult to do, though.
A second thing would be to act aggressively as an international community to stop countries when they start to oppress a minority. This is also hard to do short of war.