Sorry, that was kind of clickbait
Last summer, I had my kids start doing their tempo runs on an out and back course. The instructions are always: "Run comfortably fast and make it back in the same time that you went out (or faster)." But there are 2 caveats to keep them from racing
1. There is always some sort of tag on the end. Usually 200-300s at mile race pace or 400s at 2 mile race pace
2. If they get back to the starting line before the time is up, they have to keep on going until they've reached the prescribed time.
These factors together have helped us start to have way more effective tempo runs. I also usually stagger the starts, with the faster groups going off first, so there is no incentive for the slower groups to try and hang on to a hot pace early in the workout. We usually stagger the starts by 30 seconds, so it takes 3-4 minutes to get all of the groups started.
Here's our workout from this morning (I didn't stagger the starts, but should have because my second group of boys ended up going a bit too hard. Good workout though, all of the boys averaged 6:03 to 6:17 for 30 minutes.