Laurie,
James G. Randall once wrote "To say that Lincoln meant that the first shot would be fired by the other side
if a first shot was fired is not to say that he maneuvered to have the first shot fired."
To believe that Lincoln did this purposefully would require two things. First, to believe that Lincoln hungered for a war with the southern states and second, that everything Lincoln said up to the point when Sumter was fired upon was a lie. So far, the only consistent supporters of either claim have an unmistakable southern bias. I'm sorry, but there is absolutely no evidence for this. Your grandson's teacher is right.
No beating from me. Just cold, hard reason. As I once read,
You can have no conflict without being yourselves the aggressors.