Can’t comment about Swarthmore, but as for Carleton … well, it sort of depends on your definition of “heavy” or of “integral” [li]. However, to give some concrete data, and to drive the point home on what other posters have been saying about how common pot is on college campuses in 2017:[/li]
Marijuana use by Carleton men:
Used in past year: 54.5%
“Currently” using: 34.8%
Carleton is not on the PR “Reefer Madness” list, and yet about half the students inhale at least once a year, and apparently more than half of those students do it regularly.
About 9.6% of students reported using other drugs (5.7% using ecstasy and 5.7% using hallucinogens). (This is actually a bit lower from my era, when LSD and mushrooms were big — about 10 or 20% according to one unscientific survey conducted by the school newspaper.) Hard drug use, however, is relatively rare at Carleton (cocaine 3.2%, opiates 0.4%, e.g.).
Source: 2015 Boynton Health Service Survey Team, University of Minnesota. 2015 College Student Health Survey Report: Health and Health-Related Behaviors: Carleton College Students, pages 17-23.
The same report also gives the following nation-wide averages for weed use: 35.5% within the past year, 20.6% regularly using. So, yeah, substance-free floors are probably advisable regardless of which school OP’s son ends up choosing.
[*] Based on my experience at Carleton, there’s probably a relatively small fraction of what I’d call truly heavy users while most are less frequent users (perhaps once/twice a week on Friday/Saturday nights, or a handful of times per term at occasions like end of finals, Halloween, Mai Fete). I probably wouldn’t call it “integral” to Carleton, though I’d say exactly the same about Reed; several relatives and acquaintances of mine are Reedies, and, AFAIK, none of them use drugs!