Your change could be happening for many reasons, have a group discussion with your about the benefits of the studio environment vs. working at home.  Get some feedback and maybe you'll gain some insight into what's going on.

For me studio vs. home varied a lot by semester.   Problems/limitations with the physical environment of the studio and sometimes inconsiderate and disruptive behaviors by other students would make me decide to work at home.

I spent some time at a commuter school where lots of people worked from home.  It was a great way to cover up the fact that your parents and siblings helped you with the production of the project.  This was in the days of hand drafting and really meticulous final models;  I'm not sure how easy is to utilize ringers into today's more digital workflow.

Nobody should work late hours in studio or at home. Does the work suffer or is it just less fun for the people and professors left behind in studio? I know studio culture is great fun and a kind of rite of passage to become an architect and have great stories at diner parties but it ruins the profession at large in my opinion when people think it's normal to slave like that.

Studio culture at my old haunt seems to have gone downhill since half the classes are Chinese internationals who only talk to one another in Chinese. Cash money for the school, though.

How can I incentivise my students to work in studio?

At the school I went to, the professors would drop by at 3am, and Sat afternoon if you weren't there, then you got marked down

Students are getting increasingly competitive. Gone are the days of old where individuals would extend their knowledge to others and help each other out as part of a sharing culture. If there aren't decent PCs for rendering in the labs at school, all the more reason for them to work at home.

Do the students work on computers? If you want the studio to buzz, get them to build physical models where they have to borrow supplies from each other and look at each other's work to build actual spatial and material skills. No downloading or coyping parts without the rigor of creating them. With that being said, studio is distracting and you should be allowed to work from home sometimes too. 

Ours was a balance. You were required to be in studio from 9 to 5, on two set days per week. We had all other classes on a single day, so for at least 3 days of the week, there were plenty of people around. For those who preferred to not work in studio, they still had half the week to work elsewhere.

I do think there's value in studio culture, to a point. But that has to be balanced with the fact that people often have other conflicting priorities, learn differently, etc. 

Beyond that, I'm sure many agree that school preparing one for the workforce in architecture is a total myth. 

randomised

And you took that mentality of working with you into your professional career, right?

Absolutely - You do what it takes

 Studied architecture in San Diego - we took our cues from the Marines and the SEALSs - one of my classmates was a Commander in the Navy, her husband on SEAL team 6 - on M.arch "Hell Week" she worked non-stop for 5 days and 5 nights

Xenakis attitude and others with regard to this non stop work attitude...it's a white collar job and school is the rare time where one can explore ideas and have a modicum of freedom in thought processes. Not all thinking/work happens in the studio-in fact one could easily argue many breakthroughs occur when one steps away from the desk. Working oneself to death in school or work is not only unnecessary in this field it's incredibly counter productive as mentally intense activities such as ours required rest periods, without which one's efficiency and accuracy quickly nosedive.

To OP, by third year your students have likely started to develop their own work habits and style, and any attempt to coerce or force them to commingle will only cause them to resent you. You can suggest it's to their benefit to operate in studio, but ultimately it's their money (tuition), let them work how they wish. You can force them to turn in physical models if you must but once they finish laser cutting they'll go home or back to their part time jobs to finish the rest on the laptops. Besides they'll spend plenty of time chained to a desk crammed into a studio with other designers once they start working.

Personally I always found working in studio (school and work) to be distracting more than anything. So many people apparently there just to socialize - and not about architecture.

I've had the opposite problem at some universities in recent years: the administration, in order to maximize space, has decided to move toward a system of no dedicated studio space - so each student just has a flat file and a locker, they can't utilize the school's studio space while other scheduled classes are using it, and during evenings and weekends it's a first-come first-served system with no assigned desks.  The result is more students wanting to work at school than space available, so there's more incentive to get there first.  If I drop by on a weekend the place is packed - but usually with the same group of students who get there early and stake out their space for the day.

I agree that there's less reason these days to have to work at school.  It's not like when I was a student and there were maylines and layers and layers of trace involved.  It's not even like the early days of computers when there were three work stations at school and nobody had their own computer or software. 

Some students thrive in a collective studio environment.  Others don't.  Some groups of students in some years are more social and collaborative.  Others are more competitive, which seems to lead to more secrecy.  You as the instructor can influence some of that in the types of projects and tasks you assign, and in how you critique and grade the work.

Students do better when they work at Uni and that doesn't mean all nighters. No, you should discourage a culture of all nighters. The rise in student mental health issues are partly attributed to this culture.

A studio agenda/brief has to be designed from the start to work collaboratively/collectively. Practice works this way so why not studio. One can still have individuality and collectivity - 

Lets flip the question - how do you think you have designed the environment to develop the studio?

Ted, I'm not sure how you can contribute all nighters to a "rise" in mental health issues, since they've always existed.  Are the frequency of all nighters on the rise as well?  

OP - It would be an interesting idea to assign students a code section and require them to check another student's current scheme for code compliance.  It still might not produce more in-office activity, but they'd at least have to meet up and collaborate somewhere.  As I recall from my studio days, code compliance was always touted, especially if you made an egregious error that was caught by a prof, but never really combed through for complete compliance.  The fancier/better the student designer, the less their project had to meet a reality check.  

Where I attended undergrad, almost everyone was in studio all the time.  Probably 50% of the time was productive; the other 50% was riding skateboards down the hall, having sleep deprived dance parties, procrastinating, and napping under desks.  It was impressed upon everyone that if you're not here, you're probably not going to do well because you should be learning from your classmates by walking around and asking people what they're working on.  We had a TON of impromptu midnight student-only crits, where groups of us would go to other studios and they would present to us, and we would present to them.  It was helpful to us to get our ideas vocalized and get initial feedback, not to mention, asking about best approaches to making complex models.  The only people that weren't there frequently were the barely passing students who would hurry through things in order to be a part of other organizations.  Their grades didn't get docked for not being around; it was just that they weren't spending as much time on their physical models, or making as many iterations, therefore you could tell the end product wasn't as good as others.  That being said, every Friday and Saturday nights almost everyone left the studio to be out at parties, in bars, or at football games.  We did have a strong studio culture, but we also had professors that hosted casual grill outs at their houses/work spaces where students could go and blow off steam.

where and when I attended undergrad, it was assumed anybody studying architecture would know already everything about architecture, so teachers were not around a lot, you had to pick your classmates brains anytime you could, hence living in studio for almost 5 years.

Are you sure it's not just your current group of students? Seems possible you just got a less collaborative group of students that prefer to work at home, and it was just luck of the draw. 

Or...if you're seeing this across the board at your school and the change is only in the last year or so... I dunno I think you might need to look around and see if any policies changed or something like that. A culture shift like this that quickly sounds to me like some outside factor changed, not that the suddenly your students became dreaded Millennials (there's just something about this question that just pings my Millennial-stereotype sensor - if that's not correct, apologies). 

Maybe the building started getting locked earlier? Or the heating/cooling is sucking after 7pm? Change in school policy of some kind? Public transit schedule cuts? Do the students sense that professors are more interested in seeing pretty digital renderings than physical models, so they prioritize those, which they can do from home? 

students today want it easy and when the graduate, just want to do design and leave early - leaving all of the BIM/Cad coordination stuff to us more experienced types - doing things like sheet list and sheet set up is beneath them 

Xenakis that isn't true at all. Sure there are lazy types but that's at any age. I've met plenty of fresh grads - and was myself the same way - who are eager to learn, more than happy to do the 'boring' stuff and pour over every bit of correspondence to absorb as much as possible. Maybe you've just worked with duds. Not everyone just wants to 'design' some young people are still interested in the mechanics of actual construction. Really depends on the person. I've also run into situations, such as one of the first firms I worked at (and hated/left) where the older 'experienced' folk refused to allow the young staff to even look at coordination items much less assist in the process. I learned pretty much nothing at that place no matter how much I asked and tried to glean, and was totally miserable because of it. Sure enough I made PA not long after starting at a firm where 'experienced' people actually let me participate.

Ok this has been buggin' me since the start and since no one's going to ask, I will.

When you refer to time in "Studio", are you referring to studio sessions (w/ tutors) or spending time in that collaborative space with other students where models/renderings/drawings are done at one's own pace.

I noticed the responses may vary in accordance to the term used.

Thanks everyone for all the inputs... A repeating theme in the comments looks to be distractions as a major reason to work at home.  Friends socializing, small talk, rowdiness after hours.    I can totally see this happening and have heard this from a couple of my better students. The way I see it is that the students will pull long hours whether they work at home or in studio.  If studio is distracting many will be faster at home. The loss is what they learn from each other. For example they are learning grasshopper in studio, troubleshooting the program is sped up so much with help from fellow classmates.    
I will have to get my whole studio together to have a discussion about studio culture, distractions, production, learning, helping one another, and respect of space. 

Traditional "studio culture" was originally designed for the exclusive participation of well-to-do white male students and is a relic of the past. This "culture" is no longer in line with the reality of being a student today. There are students who need to work full-time jobs, who are parents, who are caretakers for other family members, who are dealing with visa/immigration issues, etc.  The culture needs to adapt to the needs of the students, not the other way around.

A lot of these comments have made me reflect on my experience, and it's a lot more negative than I've previously realized.

I didn't post my first attempt because it was getting too long and particular, but suffice it to say that studio culture breeds way more 'sharing' of tasks than sharing of ideas.  Usually, only a couple people know how to render nicely, or know how to use grasshopper well, and social dynamics allows some people to peer pressure others to do their work.  Most likely, the distractions that some students are complaining about aren't issues like loud music, and its definitely easier to stay at home than get pressured to help out another student with their project.

Someone asking/wanting his students stay and work in the studio after hours is just INSANE to me. 

Why is it so important? why is it an issue? For my understanding, the studios are there for students who don't have the space at their dorm/apartment to be able to use the studio space to experiment, build models, etc. It has no value in itself, the studio is there to facilitate. It's not like this is some kind of a learning experience everyone should undergo to be a good architect or whatever, and it is in NO WAY have anything to do with how an actual office work. 

I'm starting my 5th year in architecture school now, and it always bothered me when tutors use the lame ass excuse that they need to prepare us for real life in an office, so they have to suck the life out of you to do so, and exhaust you to the point where you hate everything about everyone all the time. The academia is not a work space, it's the place where you experiment, share ideas, create, make mistakes, and so on. It has nothing to do with preparing me to work in an office, when you start work in an office you learn how to do that. It's not like you're on a mission to Mars, it's architecture, the most overhyped and irrelevant profession there is, it's just an office. Seriously, just a fucking office. You'll get the point of how it works after a month or so working there, and if not you're just an idiot and shouldn't waste everybody's time. 

And it's 2017. Means of communication and sharing have changed a lot. I don't need to be in the same place as my mate to ask him about something or giving advice to someone. To act like studio culture has merits in itself is just plain moronic. It facilitates, that's it.

"I don't need to be in the same place as my mate to ask him about something or giving advice to someone."

I disagree. I think physical proximity facilitates the kind of incidental interactions that lead to more creative output.

"The academia is not a work space, it's the place where you experiment, share ideas, create, make mistakes, and so on."

Exactly, and that sort of experimentation and sharing - in my luddite opinion - is best done in a shared physical environment where spontaneity can lead to real problem solving. 

I will back you up that "preparing you for office life" is a bullshit excuse. I've never worked nearly half as intensely in the office as I did in studio, and no one should have to. But the benefits of "studio culture" that I found went way beyond preparation for the occasional 60 hour deadline week. I not only had some of my best ideas while procrastinating with other strung out students, I built some of my most solid friendships and mentorships by commiserating and bonding in that shared experience.

Maybe I'm old fashioned (I'm not even that old) but I don't think that experience can be replaced by digital communication.

having a beer fridge, lounge area, and small kitchenette in our studio worked wonders.

In related news, I heard realtors are going to start adopting the all-night studio culture to further their profession too. Students of real estate are now expected to stay up all night taking awkward, poorly-lit and disproportionate photos, lighting sugar cookie scented candles, and writing simple, pleasing phrases like, "It's a charmer!" Some advanced students will be chosen to practice printing and collating forms.