The strategy that is optimal physically isn't necessarily the same strategy that is optimal mentally/emotionally.
Most young runners aren't fully invested in the sport. They're trying it out. When it hurts, they back off. They find little motivation in being at the back of the back. In a video game they want to quit and start over if the game isn't going well. Expecting them to have the confidence to go out slow and pick up the pace is likely to lead to disappointment among inexperienced runners. That disappointment can prevent longer term engagement in the sport that is helpful in developing more effective strategies.
If you have established a culture on your team where the best, most experienced runners, do run even splits, then that culture can be a powerful tool for the younger, least experienced, runners to develop the confidence necessary to go out slower and move up. Role models are important.
I cringe when people talk about "pace" in a cross-country race. There are certainly a multitude of courses that are essentially track on grass, but you still potentially have mud, wind, etc. that have real impacts that can differ along the route.
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One possible approach for younger runners:
Early in the season it's difficult to know how good other teams are going to be or even what teams are going to be at some invitationals. However, it's pretty rare that there are huge changes from one year to another in the overall distribution of times, unless conditions are significantly different.
As a coach you should be able to figure out roughly where you would like each kid to finish within a field. Set a goal to be near that position by the mile, then set incentives for them to move up after that. Send two volunteers to the mile mark. Have one count runners and the other record on paper or on video the places of each runner on your team. Then compare that to finish places. Provide some type of reward/recognition for those who have finished at/near their goal place and who also improved their overall place from the 1st mile to the finish.
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As your runners mature, they should be able to develop a broad array of strategies they can use to optimize their place.
Even/negative splits may be the best strategy in most situations when the course is flat and firm and little wind, but how often do those conditions really exist - that depends a lot on where you live/race.
For those that would argue, that the "effort" should increase as if you were running a flat, fast course on a windless day - that's an abstraction that is not going to translate well to most young runners.
My recommendation is to use training to get them to know what the first mile should feel like. Use that combined with a goal for roughly what place they should be in at the mile. Have them focus on competing after that in the race.
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Note: There are some great invitationals that create a horrible situation for JV runners. They might allow 7-10 runners in the varsity race and then put everyone else into the JV/Open race. The varsity race might have 200-300 kids, which the course might handle fine, but when you put 700+ kids in the JV/Open race on the same course the idea of running even splits isn't remotely optimal. The first two miles feel like you're in the school hallway changing classes - passing people is a matter of changing gears over and over. It's certainly not optimal physically, and it's brutal mentally.