I don't want to minimize the tragic death of the young lad, however:

The teachers would argue that if they had actually banned the kids who couldn't swim from the trip that they would have faced complaints about the unfairness of it all. (After all, nobody fails anything anymore in Ontario schools; it hurts people's self-esteem.) 

The parents of poorer kids would argue that they can't afford the time, travel, or expense of going to swimming pools and to teach their children how to swim. (After all that is the preserve of the middle class.) 

The school administrators will argue that there isn't enough money or time to teach skills like swimming. (After all they are spending so much time teaching kids the three R's that so many of them aren't learning anyway.) 

(If I was a teacher that would be the last time that I had anything to do with any school trips, and that is most likely what will happen here.  Why risk it?)

And the big losers will be the inner-city kids who never get out.