Area of focus (4x100m): Our first leg is going to be the best starter on the team. This person may not necessarily be the fastest but they clear the blocks well and can accelerate pretty good through 60m. Our second leg is typically our fastest leg.
The reason we put the top sprinter here is because on most HS teams the difference between your top guy/girl and the rest of the pack can be a big difference. I'm talking 10.4-11.0 difference. Putting that type of speed last may cost us being out of the race before it even gets to them. With the "Horse" going second we either give the third leg a lead or at least we'll hold good position in the race.
Also we don't want our top sprinter straining too much trying to run the entire field down every race - recipe for injury! Our third leg typically is a good 200m runner or anyone that can not only handle running the curve but is great at receiving and passing the baton. The anchor leg is the next best guy with the most confidence. Again not typically your fastest athlete but one that believes they can win any race. Most of all understand that's is not about how fast the individual athlete can run the 100m but, how fast can the team of four get that baton around the track.
When we have run-offs for relay spots we run 120m. If you can run 120 that shows that you can run through the zones. Being able to run through the zones keeps the baton moving with little wasted time during the exchange.