Then someone explained it using a pie example, and OP got it, and said that s/he'd never had it explained like that.
My teacher cut up apples to show us fractions in grade 2 (age 7-8). I never thought of my school system as being very competent -- maybe it was only my teachers who rocked.
I also taught myself how to work mod 7 without knowing what I was really doing in grade 7 (age 12-13). The example was something like "Today is Tuesday. What day of the week will it be in 38 days?" We did the examples on our own, and then the teacher took them up. She used a visual proof, by drawing a calendar and counting. When she was finished, I politely asked if I could show the class how I did it -- I had subtracted off 7 until I had a remainder, and then counted forward three days. She praised and thanked me for my explanation.
In grade 8, the teacher couldn't get through to my class about intro to algebra (x+3=7 -- what's x?) so I got up and did it (and he let me).
That same year though, we had a substitute teacher who was NASTY. We had to measure line segments from our textbook with those cheap rulers you get with geometry sets, and we had to do it to tenths of a millimeter. You can't get that accuracy from those rulers. She marked it wrong if it didn't match the textbook, and when I told her the rulers were different, she looked at me and yelled "Rulers are NOT different!" (I had held two up together and they were so cheap they didn't line up at .5 millimeters after about 3cm)
But even though my pre-secondary-schools had the same teacher for all subjects, it usually worked out.