Almost all of us start going to school when we’re three or four, and we don’t stop until we’re somewhere between 18 and 22. Some of us, having nothing better to do, keep going to school long into our twenties and beyond.
And yet, invariably, most of what we learn vanishes. We keep a few things: multiplication, spelling, “Columbus sailed the ocean blue in fourteen-hundred and ninety-two.” But if we had to retake the exams, we’d flunk.
Just how fast do we lose our learning? You could do the responsible thing and consult Table 1 of this review paper and find that a) studies rarely follow up more than a year later to see what people remember, b) for the studies that do look at longer spans of time, people can lose anywhere between 14% and 85% of their knowledge in just a few years, and c) it depends on all kinds of factors, like the subject, how people are tested, and whether they ever used the material between learning and recall.
Or, you could just watch this episode of Are You Smarter Than a 5th Grader? where a grown woman stands in the midst of horrified 10-year-olds and shouts, “THERE’S THREE-HUNDRED AND FIFTY-TWO FEET IN A YARD!”