I’ve claimed that for years (for example with wave watching, with active lunch breaks, with tweeting about course content), but now I read the current iEarth Journal Club article that makes the exact same point and explains it with expectancy-value theory. See my 2014 summary of Hulleman & Harackiewicz (2009), or even better, read the 2-page-long original article!

Hulleman, C. S., & Harackiewicz, J. M. (2009). Promoting interest and performance in high school science classes. science, 326(5958), 1410-1412.