Is this an effective way to get a girl I coach to run a sub 5 mile?

That will make her mentally weak. Once you drop out of a race once it gets way easier to do, and because of that it gets way harder to dig deep when she'll have to at the end of the race to break 5:00.

Kids like to win races and help their teams to win meets. Dropping out will not help your girl to do either of those. Have her work on different aspects of her race in the duals. Getting out hard, surging in the middle, kicking off a moderate pace. All of these aspects can be worked on individually.

I have never felt that dual meets were conducive to fast times. My kids usually double or even triple in duals in an attempt to get the team win. My better kids are able to use the races as workouts.

When you want her to run fast, get her into an invitational with a bunch of girls that are right around the 5 minute mark and watch the magic happen.

What did she do to get to 5:08 last year? That seemed to work okay...

If it was you who got her there, keep the same basic approach. Though girls "naturally" progress from junior to senior less often than boys do, she should still get under five by doing much of the same things.

If it was someone else who got her to 5:08, find out what he/she/they did to get the girl there, and try to keep most of that in her training this year.

I do understand the logic of staying with goal pace as long as one can, and I actually did some stuff (time trials) like that in my own training, but it's psychologically very tough--you keep getting confronted by failure at your goal pace.

I guess I agree with a poster above: orient everything toward teaching her to "run to win," and then in duals you can prescribe a variety of scenarios. Let her know that she gets to "practice" different approaches in duals so that she'll be ready to win in the big meets; then get her to big meets wherein winning will mean that she has to go sub-five!

[And maybe take a Lydiard approach to race selection during the season. If she keeps a good steady pace and can run 77-80 all day long, but looks to be awkward or working really hard at 73-75 pace, then mix in some shorter races: 800s or even 400s, maybe on the relay.

[On the other hand, if she looks super going out at 73-75, but slows 'way down after 800 or 1000m, then mix in some 3200m races.]