When I was a sophomore I only had a 5k pr of 18:08, but at my dirt slow school that was enough to net me the school record by around 30 seconds, and that made me think I was actually fast.
I didn't have a race plan going into the area meet that year, so I had no idea how fast to go out or where to position myself. Our area meet is generally one of the more competitive meets in the state, and featured some locally impressive names. When the gun went off I went for it and tucked into the lead pack of four (All seniors at the time, of whom two are running at UGA and one of whom is running at Furman). We went through the mile in 5:04, which shattered my mediocre 5:08 pr.
The next mile was downhill, and they went ~5:05, I believe, but I could only handle a 6:04. The last mile was a very steep uphill, and the winner closed in 5:12 for 15:55. I however, was deep in oxygen debt and collapsed at 2.5 miles. I got back up and walked it in for a 23:45, but the JV race had already started by the time I finished. It was a by far my worst high school race.
Just for reference, I'm now a senior and ranked 4th in the state.