the two paragraphs above showing that the offending letters were the minority, together with the principles comment that they would "never censor" (which is proper), shows that they the 'error' was probably in not giving proper instruction to the students in the first place. Further, some 'screening' could be done as well, encouraging the students to simply not write if they have anything negative on thier mind.
Sad event .. but not sure if the teacher is 'guilty' of anything other than bad planning and follow-through on what should have been a positive experience for both students and soldiers.
Yes, although perhaps the teacher should have sent a cover letter explaining the situation. Open peaceful disagreement with another's point of view is a cherished freedom to be enjoyed. Perhaps the teacher did send such a letter, but it was misplaced or ignored.
By 6th grade, most public school students likely to have been captive audiences for up to 7 years of liberal indoctrination. Also, the largest determinant of behavior at that age is peer pressure more than anything else. That the soldier got any letters of support at all is a cause for celebration of sorts-- the indoctrination is not having a uniformly negative effect.