I looked at your world and I didn't see any code to make the fish or shark move.
To move all of the things in the school:
-Put in the movement code you need like "Fish move forward 1 meter", for example
-Put in a "For all together" that is referring to the "School" list
-Place the movement code you made into the "for all together"
-Replace the objects in your movement code with the "item_from_school" in your "for all together"
All of the fish and the shark should move forward 1 meter.
Make whatever changes you need!
==============Some of my Games and Ideas===========
Sky Warrior: http://www.alice.org/community/showthread.php?t=6291
Health Bars: http://www.alice.org/community/showthread.php?p=36968#post36968
Sky Warrior: Dual Force: http://www.alice.org/community/showthread.php?t=7174
Want to make your own space game? http://www.alice.org/community/showthread.php?t=6389