Hey Karl, If the 15 and 17 year old return, you should ask them if they plan on going to university when they're done high school. I'm going out on a limb here and presume their answer will be 'no'.
Then show them that quote from the 1969 Awake! magazine when they told everyone nearly 40 years ago that education was a waste of time and that they'd "never grow old in this system of things". Might make them stop and think.