Unsatisfied at the lack of hard numbers we've got for military training, I'm running experiments with Dwarf Therapist to see exactly how much EXP is being gained. During the process, I found a curious 'feature' of training: designations screw with training. Now we've known since the 40d days that things still happen (e.g. cats adopting owners) while you're designating areas to be mined out or chopped down (greatly accelerated by using a mouse). It's a very useful trick to get merchants to get organised quickly (remember the nuclear warthog days of early DF2010?) and get the liaison business out of the way in an instant. It also affects sleep/drink/eat needs apparently as well as the actual act of drinking from my observations - I've gotten dwarves to finish drinking instantly without any time steps passing and they've gotten thirsty/sleepy while I was designating too.
Now here's my main discovery: designations reduce the duration of training activities without real time passing. For "Individual Weapon Drill" and "Spar", this is very bad as those require real time to pass to gather EXP. They gain a minor amount and then they go into this weird "Individual Weapon Drill/Resting" job. However, demonstrations DO transfer EXP without real time passing.
I'll edit this post later as I gather more details and organise my data.
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Ok so I had 2 dwarves with 0 skill (7 peasant embark) and set them to train in a 2-man squad. There are 3 things soldiers with that order can do: drills, demonstrations and sparring. The practice of spamming designations to quickly finish off an activity will be referred to as "insta-accelerating". I only observed weapon skill, Fighter and Dodge - the other defensive skills do go up slowly like Dodge.
--- Weapon Drill
Ever since the early DF2010 days when this was the only training that worked properly, we've known it was horrendously slow at gathering EXP. I'd say this is the main reason why danger rooms were invented - they were essential back in the days as you had to avoid telling dwarves to actively train.
1 day of doing drills gives ~12 EXP in Fighter and their weapon skill. They may also get +3 EXP in Dodge.
Insta-accelerated, the weapon drill ends with 5 EXP in Fighter/Weapon learnt.
--- Sparring
Not every action you read in the sparring combat log yields EXP. It seems to be random whether a dwarf learns from a sparring move or not.
1 day of sparring thus has a varied EXP gain rate: I've seen +5 EXP and I've seen +100 in Weapon skill. Fighter goes up faster as any melee skill being trained also trains this skill (i.e. shield bashing, punching, etc): again, I've seen +20 and +200 on different days.
Dodging goes up much more slowly, typically some +6 EXP per day though some days it doesn't go up at all.
Insta-accelerated sparring yields: +8~40 Fighter, +1~30 Weapon, +0~5 Dodge with the distribution heavily weighted towards the lower end of those ranges.
--- Demonstrations
EXP is given out at set intervals in demonstrations. For the sake of argument, I shall refer to these intervals as "lessons".
For Teacher 0 & Student 0 soldiers, there are an average of 3.5 lessons per day and each lesson yields:
+10 Student, +15 Taught Skill for the student
+10 Teacher, +5 Taught Skill for the teacher
I've had a case where the teacher had less EXP to start the training session though he did have the same rank as the student.
When insta-accelerated, something odd happened: both teacher and student gained +150 Teacher, +150 Student, +300 Taught Skill.
Conclusion: overall, insta-accelerating is bad for military training. Sparring is where soldiers learn to wield their weapons properly and you want it to last as long as possible. Demonstrations could be exploited if it's in a hard-to-learn skill (any of the defensive skills).