A lot of people have strong feelings about internships, but as this great EPI chart shows those feelings aren't actually based on anything because the government agencies we count on to produce labor market data don't have any information about them. That, above, is everything the Census Bureau, the Bureau of Labor Statistics, and the Bureau of Economic Analysis know about internships.
How many people are interning at any given time? How many hours do they work? What if anything do they get paid? How many of them are concurrently in school? Nobody knows!