I just found this video commentary on Sumer is Icumen In, by James Hargreaves:

The oldest surviving song in English is not what I expected

As soon as I saw the title of the video I knew which song he meant. We learned this in school and sang it in rounds, like the performance at the end of the video. I've always loved it, and it probably had a strong influence on my decision to study Chaucer's Canterbury Tales in later high school - on my own, in the library because no-one else in the class was interested - and also Old and Middle English literature at university.