Well they are known to be party ships..This sounds sort of like the school arranged this group cruise..and usually when a large load of kids go on a cruise, the line that is picked is Carnival.
Two reasons I possibly won't run into this type of situation..
I will never cruise while kids are out of school and I will never again cruise on a mass market line.
In the future maybe moving your vacation to a more quiet time would help.
The letter you received is probaly a standard letter they send to all customers who had issues with their cruise..I assure you not much will change.
Also for your info...posted on you tube is a video of a large group of kids who graduated from a school in Atlanta..the line was Carnival...and they were out of control...yelling, screaming cursing and acting like gangsters.
Im really not surprised this happened on Carnival...In fact if you type in "fight on cruise ship" you will see fights that broke out on you guessed it.."Carnival".