Then the teachers can simply teach that basic rights are INHERENT within the condition of being a human being. All persons have these rights by virtue of birth. They reside within each individual and cannot be restricted or taken away by anyone. We were all Born Free before there were any governments at all, anywhere.
If such can be claimed for animals, then, as animals, ourselves, such can be claimed for humans. No need to invoke Deity and no need to even mention Deity. This totally defangs the atheists. After all, they have rights, too, without believing in God.
It is not as easy as you suggest. What do you say when a student says, "then why did no one recognize these human rights for all those many years throughout the history of the world? And why do many countries even today not recognize them (and to this 2nd question you cannot point out that people that do not believe in God as their supreme being, have someone else that they look to as being "supreme" and thus ruling over them.
For, you see,if we cannot explain that the right is given (granted) by God, and we say it just "is" then the students cannot quite fathom how something just is, with no authority behind it. For instance, I can say, "I own this house, I am a homeowner." But in reality without a proper deed to show as evidence and authority, how would I be believed if questioned? I cannot just say, "I was just born with it, inherited it." Rather I need some entity with proper authority to back me up. Thus we cannot leave God out of the equation when we claim inalienable rights.
America was founded upon the concept of the God of the Bible, and atheist can deny that all they want, but it does not change the facts. The government the founders set up allows people to chose to worship other than our God, or even to not worship any god. But they did not foresee a future where the God-less would actually be able to take over the country.