这信可以这样的写：

Dear Dr. XXXX 校长
After talk with my son, I found out that it is not A (my son) who started the fight, it is B (the other student) who started the fight. I take back my apologies that I did yesterday.
We ask for the apology from B. We also ask the school to ensure that such thing will never happen again.
Respectfully,

XXX

所有跟帖： 

• 这样不行的 -liveinca- ♀ (0 bytes) () 04/01/2015 postreply 09:21:54

• 对。这样绝对不行。道歉了怎么能take back, 这不是耍弄principal嘛，学校要生气的，不利于事情的解决。 -swj2000- ♀ (0 bytes) () 04/01/2015 postreply 10:16:59

• +1 -LittleHer- ♀ (0 bytes) () 04/01/2015 postreply 09:23:50

• 最重要的要提出在学校下结论前，所有涉事方坐下来，面对面谈清楚事情原由。 -keessa- ♀ (0 bytes) () 04/01/2015 postreply 09:28:37

• 不需要收回道歉，但是一定要坚持那个日本孩子道歉。 -超級良民- ♀ (0 bytes) () 04/01/2015 postreply 09:37:30