Yes, he still qualifies as your dependent. The co-op (or internship) time is a school-approved program for which academic credit was granted, and counts as full time attendance (since he was full time for the previous academic session).
For more on this subject, see this previous discussion. https://ttlc.intuit.com/community/college-education/discussion/my-20-years-old-son-living-with-me-at...
