Very few high school athletes will have enough of an aerobic base to use the conversions from mile PR to LT or AT paces. In the fall while they are running 5k's, I use Daniels charts to determine tempo paces based on their 5k XC times on a flat course.
Our tempos are usually done on firm surfaces so their tempo pace would be adjusted down, but we also usually use training flats rather than racing flats which would adjust times up. In the end, I figure the firm surfaces and heavier shoes are a wash with regard to their effects on tempo paces. If we do a tempo run on the track, I have found that 4800m in training flats should be completed in about the same time as their 5000m time on a typical XC course. For the faster kids, they may have to run a bit further than 4800 to get in a run of at least 20 minutes, but the pace is still the same.
In the winter/spring, determining tempo paces is not so formulaic. During Jan/Feb, my first priority is to get the kids to run consistent, negative, splits for a firm continuous run of 20-25 minutes. By the time they figure out how to do this, I think most have naturally found an appropriate tempo pace. There's not much else you can do when everything is under a foot of snow and they haven't raced for several months. To encourage progression, I suggest the kids start the first mile of a tempo run at the pace they averaged for their previous tempo run. If they then run negative splits, it sets them up for a slightly faster future tempo run.
For the more advanced kids that have a pretty well developed aerobic system and have continued running since XC season was over, we use the paces established by Daniels based on their 5k XC time for their first couple tempo workouts, but then go by feel - always requiring negative splits, however. This usually works out to ~mile PR + ~50 seconds for a sub-16 5k guy and mile PR + ~60 seconds for an 18-minute 5k guy.
These paces are fairly good when the weather is decent, but that situation is the exception rather than the rule during the winter. Hence, I really try to get the kids to think about what tempo pace FEELS like and then when the weather conditions are bad I tell them to run at tempo EFFORT.
Once meets start in the spring, I'll have the advanced kids get in tempo work before the a meet and then during the meet by running the 3200m at a prescribed pace. They will also run the 4x400 immediately after this. The 2nd and 3rd tier kids will usually do tempo work on Fridays, since they usually will not be running in the Saturday Invitationals and will be racing hard in the week-day dual meets.
A typical (ideal?) week during the dual meet season might look like this:
M - Intervals (200m-800m)
Tu- Aerobic run + 4-6 x 150m pick-ups
W - Dual Meet (1st tier - tempo; 2nd/3rd tier - Rep)
Th - longer Aerobic run (= weekly long run for 2nd/3rd tier runners that aren't likely to run on their own over the weekend)
F - Short aerobic run for 1st tier/Tempo workout for 2nd/3rd tier
Sa - Invitational (1st tier - Rep work; aerobic run for 2nd/3rd tier, hopefully!)
Su - Long run at relaxed pace for 1st tier. Off day or short aerobic run for 2nd/3rd tier.
* Getting in tempo work during dual meets can be challenging and is dependent on circumstances. It is not unusual to end up with a mix of tempo and a little rep work for the 1st tier.
Once the dual meet season ends and Championship season begins, our meets fall on Wednesday and/or Friday. If the meet is on Friday, we may do a race simulation workout on Monday with a short tempo workout on Wednesday. If the race is on Wednesday, we'll do a light tempo workout on Monday and may do a simulation workout on Saturday. Simulation workouts are very dependent on the individual, but are at race pace and max out with a total volume of 1600m for an 800m runner up to 3200m for a miler/2-miler.
For example an 800m runner might do 600m/30 sec rest/200m at race pace take a 15-20 minute break and repeat. A 3200m runner might do 3x1000m at race pace with 200m jog recoveries. The exact content of the simulation will be highly dependent on what each individual needs to work on. If things have been going well, a miler might come in Saturday morning, warm-up, do 4x400 at goal race pace with 60 second recoveries, do a short cool-down and go home.
During this championship phase, I almost always limit the tempo runs to 3 miles even though it's less than the recommended 20 minute usually associated with tempo runs. I just want to challenge their systems enough to maintain the aerobic fitness they've already obtained. Longer tempo workouts are reserved for the late base phase and the pre-comp phase.
...I had no intention of writing this much, so I apologize if this is a bit incoherent. I hope someone is able to get something out of this. The rest of you flame away.