are we seriously comparing a little 3 on 3 pickup in the driveway after the XC /TF meet or soccer game, with double threshold? you don't even know what you're talking about, then.
we're talking about having beginner HS kids running 2 a days with both workouts being intense interval type stuff, twice a week. when my HS did 2 a days, if one was mile intervals, the other was in a pool, or a long run, or fartlek, anything but more intervals.