is double threshold worth it in high school?

I say go for it while you can.

Possibly if the mileage is low enough.
4/4 could make you fit (that’s 2x 23-24’ runs$ but 8/8 would be silly. Better to focus on bringing down overall training pace.

Threshold is outdated terminology. Nebulous at best, simplistic at worst. No magic paces, the individual difference are relatively large, formulas more ballpark than precise and the science a bit dubious. Most Many athletes would be better served with fartlek or reps vs continuous work.

i ran around 60-65 mile weeks this winter, so keeping mileage around there maybe a little higher but no higher than 70. Would double workouts with a long. run be any better than having one longer tempo run and one shorter lt paced run with a long run and medium long run mixed in

What’s your PR? The answer is very diffferent for a sub 9:00 athlete than a 10:00 hobbyjogger

at 50 to 60 miles, it doesn't seem necessary. Once you are in that 70+ range, and you are looking at close to 15 miles per week of threshold, the doubles start to sound like a good idea. At that mileage, one double threshold in a week is probably enough. the double double feels more appropriate over 100 miles to me.

so maybe a day with 4 in the am/5 in the pm. and a separate day with 6 in one session.

This is the answer. I’d also add that everyone benefits from threshold work but the level of response will differ from athlete to athlete and so should the emphasis in training. Everyone is different. Jakob clearly is a high responder to threshold training. Not everyone is Jakob.

It also depends on where you are coming from. Been doing 6x1 mile and 10x1000 for 16 weeks? Sure start doubling to add more volume. Personally I think the above and a few short hills is plenty for the summer. Want to do more? Get in some more easy miles. The benefits of getting up to that 70-80 range is a ton for most kids and is sort of low hanging fruit compared to running double threshold.

Yes and no, if you want to do it properly you need to be doing high mileage and have a lactate meter otherwise forget it

Do you mean twice in one day? Or twice in one week?

Twice in one week is a great idea for the summer, although I'd recommend making one of the sessions a fartlek or continuous tempo with some hills, and the other session cruise intervals on flat terrain or a track.

Twice in one day is only appropriate if your single-session volume is too high to continue raising it. Usually around 8-10 miles, because that's the point where your body really starts to struggle to handle the volume (although I am familiar with people who have done as much as 15 miles in a single session).

I would guess you are not at that point, so I would recommend doing two sessions per week (with no other workouts except maybe some short hill repeats) and try to work your way up to 5-6 miles of threshold per session.

What do you suppose Jakob Ingebrigtsen was doing at that age?

Progressing from what he had done over the previous 7 years. If OP has done all of those years of base work, he can worry about what JI did...

No one should be doing it. Why on earth are you thinking of it. Explain this concept are you interested in?

To improve and run faster absolutely! as long as you have built up to the training load gradually. I did doubles in HS and improved every year. Probably ran too fast so pay attention to your true threshold pace.

ps I ran 15 min for 5k XC and more