The midwestern high school where I teach math has a rich history. Gothic architecture, a fair number of well-known former students, and a yearly enrollment of about 2,000 kids.
In one of my 9th grade algebra classes, we had a homework assignment on decimals. We had been working on rounding, truncating, and the like– practicing everything to the thousandths. For those of you that have been out of high school a while, that means rounding to the third digit. So 123.8408 becomes 123.841. Simple enough. As per routine, we begin class by self-grading homework– I call out the answers, students mark their papers, score goes at the top. Afterwards I collect them. One day while sorting through the stack and recording grades I notice this: 
Obviously, there was something lacking in performance on the assignment and I couldn’t help but think that I might have harped a little too much on the third decimal place. On the other hand, the student did round correctly…
