I think you knocked that strawman right over; nice job.
As you know, public schools are openly hostile to any hint of religious expression including the wearing of a tiny cross, Star of David or probably even a crescent moon pin. Secular Humanism is the 'new' religion and the teaching of evolution does not do much for most Christians. Not that creation was ever taught in public schools as far as I can recall. I do know that teachers have gotten into official hot water simply for reading a bible in an empty classroom during a scheduled lunch break. Enforced atheism? Not literally, but hostile and anti-religious might be an apt description. Even simple patriotism is frowned on in some school districts. The loony left has won via the NEA and the slightest whiff of religion is forbidden.
Absurd that parents/taxpayers have let this come to pass but they did and we're stuck with it for a long time to come. My hope is that the rise of private secular and religious schools and the big jump in homeschooling will have an effect that will eventually tamp down the loony left's stranglehold on our public schools and at least open them up to the acknowledgment of religion in American life as they once did. Teaching kids how to actually read, write and do math would be nice, too.
Has there ever been a school in this country that forces students to say, "I believe that Jesus is the Son of G-d?"
By your definition, that would be enforced Christianity. I know of no case on record.
Current legal thought is that if the tenets of a religious belief are stated in such a way that school sanction can be inferred, that will pressure a child since the school is seen as an authority figure. Call it pressure or coercion - it is a type of force. Thus, the ACLU put a stop to the government enforcing Christianity. Whether you agree with that thinking or not, that's how our law is currently crafted.
Under that interpretation, atheism is, indeed, enforced.
Shalom.