By the latter half of the 19th century, chalkboards had become increasingly common in classrooms; for students, the impact of watching a sentence take shape on that large surface as a comprehensible, often elegant, and sometimes downright ingenious drawing must have been significant. It’s hard to believe anyone but the most dedicated pedant could have actually enjoyed parsing, but plenty of students — including me — loved diagramming.
Me too. It’s funny: I don’t have any feeling at all that today’s students need to learn the pencil-and-paper algorithm for long division or square root extraction. But the vanishing of sentence diagrams makes me sad. Presumably if I were a linguist instead of a mathematician I’d feel the opposite.