I have heard of the Oregon workout that Pre was said to do: 30-40's. He apparently would run as long as he could alternating 200's in 30/40. It is said that he could go 3 miles.
So that got me to thinking if this is something my high school kids could do. They seemed to have a hard time "changing gears" in races. So I modified it to fit my kids: We did 3 x mile of 45-35 with the boys and 42-50 with the girls. It went really well. The hard segments are just about date mile pace for them and the slow one a little slower than AT. Physiologically I can't guarentee of the benefits, but mentally they were a little tougher.
Good session?