Maybe you guys should by a heart rate monitor this summer run most miles painfully slow at 125 - 135 heart rate, run 2 tempo's a week at 170 - 175 and one day of 6 by 30 seconds all out with jog rest. If you still only manage 27 minutes then better become a 200 meter runner.
the heart rate numbers are off maybe for you but anyways:
maximal heart rate - 70 to - 60 for the easy runs (30' - 90')
maximal heart rate - 20 to - 25 for the hard runs (20' - 30')
Sprints all out but with 3 minutes jogs in between.
Now head out and run for hours and hours a week.
By the end of the summer you guys should break 30 minutes for 10 km if you did it right. You guys probably run your easy runs just to hard. And At a point even 6'/mile is to fast for the easy runs on your engine. But if you build your aerobic engine from ground up again by the end of the summer you might do your tempo runs at 4'50" - 5'/mile. I did when i ran 4'18' for 1600m. But on my way i started painfully slow at 10 min/mile and tempo's at 6'20"/mile. Btw i didn't even do speed work back then. Just the tempo's, easy runs, sprints(30s) once a week and cross training.
Trust