A few quick things - the first is to use "exam" instead of "practice" as stated above. I think the whole community could retire if we each had a nickel for every one of us that has made that mistake.
On the AA training, my crew passes 100% of the time. The only time I have failed that mission is when I try to man the guns myself. Even Bernard shoots straighter than I do.
As for the torpedo mission, I advise that instead of immediately shooting at the ships nearby, you take the few seconds required to go the chart table and plot the course of all the ships in the area. That way after you take out the closest ships you know where to pursue the others. As I recall, some of the ships are required and some are optional, so focus only on the required ones as detailed in the mission briefing. The ships will "disappear" if you don't get to them fast enough, so put your boot into it.
On the convoy mission, although it is a bogus way to do it, you can take out the escorts easily with your deck gun and then play at will with the merchants.
Lastly, I would guess that if you are having any other troubles passing you could lower the realism levels temporarily to get through the school, then increase them back to the levels you want to play with.
Bottom line is that in order to "graduate" and get my 1500 points I used a bunch of tactics that I have never once repeated in a mission.
