Stay in School!

Ever since the boys were little they have admired construction sites. Big ones with large equipment. Two guys working on fancy brickwork for a sidewalk. Anything with tools and concrete and they stop to stare. More so as preschoolers but even today they will ogle at the men (and aren't they usually men?) in hard hats and work boots.

Back when they were three years old we walked by two men laying brickwork for a sidewalk. I was commending their craftsmanship when one of them held up his hand, pointed at my boys and said sternly to them "stay in school!" while the other gentleman nodded with great seriousness. As if three year olds understood what they were saying.

Fast forward six years later and this fall the boys and I, along with their 5 year old sister, looked up as we saw several men restore a smoke stack at an old brewery. The cherry picker was lifting a man up to on it. We stopped to admire both the work and the thrill of the rising equipment. Once again, the lift rider yelled down to my kids (we were the only people watching) "stay in school!" while several colleagues shouted in agreement.

Is there some pact that all construction workers sign to yell "stay in school!" at young children? Is there something embarrassing about working in construction?

Why does this keep happening?