If you, like me, were a nerdy type-A personality at school, you probably loathed getting put into groups for assignments. Inevitably, you'd be stuck with some bunch of lazy idiots who could credibly commit to either:
a) not caring if they got a terrible grade, and hence being uninterested in working, or
b) not being capable of getting a good grade even if they did work.
Both of these would get you to the most common outcome - the smart kid does all the work, usually ostentatiously announcing beforehand that the dumb kid is going to screw it up and thus insisting that he leave it alone, all the while still resenting the dumb kid for his idleness. The dumb kid laughs at the smart conscientious kid slaving away like a sucker.
Teachers would always spin you a bunch of junk about this being useful preparation for the real world, and how it was important for you to learn to work with people you didn't necessarily pick.
Looking back now, I realise that this was all a crock of crap - school group assignments prepare you for nothing useful, and all the irritation you felt was in fact completely justified.
The standard complaint is that you're being allocated into groups you didn't pick, and with hugely varying levels of skill. Neither of these really describes the real world. You get to pick the company you work for, even if you don't get to choose who is on every project with you. That said, it's highly unlikely that any semi-competent manager would lump together one guy who knows what he's doing and a bunch of morons who don't. Hopefully, there's a minimum level of competence required to maintain gainful employment, and you're unlikely to be stuck with someone truly awful.
That said though, it's become increasingly obvious that this isn't the real problem that makes school projects uniquely worse than real-life group projects.
No, the real problem with school projects is the following:
Everyone has accountability, but nobody has authority.
In other words, everyone is responsible for the performance of the group, but nobody has the authority to actually order anyone to do anything. If someone does a bad job, or hands things in late, or generally is so clueless that you'd rather do it yourself, there's not much you can do. If it gets really bad, you can complain to the teacher. But they generally don't want to deal with your whinging.
The assumption is that general social sanction for shirking, combined with the fact that everyone needs to work together to get the marks, should be enough to make it work. But isn't it obvious that setting up a mini-communist state for mark allocation is always going to produce a free-rider problem? And that the equilibrium is going to be that the guy who cares about it more does all the work?
This is like some Frankenstein version of real world group tasks. In most corporate settings, you're going to have a boss or team leader who is directly responsible for the team's performance, and can order people to do certain things on pain of getting fired. Hand the report in on Friday at 12pm or you get canned. Simple enough. Your boss may be an idiot, in which case it's a huge pain (of a very different sort). But at least there is a single person with the incentives to see the group succeed, and the authority to make it happen and solve the co-ordination problem.
If people get to pick their own groups and there's multiple assignments, the repeated game aspect can deter shirking somewhat.
But in general, teachers create a horrible system for assignments that simply teaches smart kids that the world is full of moochers, and that you'll end up doing a disproportionate share of the work only to see some slacker enjoy the fruits of your labour.
You might argue that this lesson is crucial for teaching them about the operation of the tax system and pork-barrel public-sector employment, and I wouldn't necessarily disagree.
I'd like to think that this was the well-thought-out plan all along, but somehow I doubt it. The only way to fund these taxes is to have businesses whose internal team dynamics are so different that productivity results and there's a surplus to be stolen in the first place.