A kid asked me what mass was. Just out of the blue.
I tried to explain. It's just the measure of matter, as height and weight are measures. But how is it different from weight, they want to know.
At this point, it gets strange. Insofar as weight!=mass, the distinction is that mass is how we think of weight and weight is something much more complicated. We're all backwards. It's silly that a six-year-old knows what weight is--in a rough intuitive sense--but not what mass is. We should stop talking in terms of weight. I don't care that I weigh 63KG at the Earth's surface, or that the bag of salt I'm buying weighs 80LB at sea level. What's actually relevant is how much of me or of salt there is. The mass. (Actually, according to Wikipedia, in commerce, 'weight' means mass. So use the term 'mass', darn it!)
Instead of having kids grow up possessing (or thinking they posess) an intuitive sense of what weight is and only teaching mass in science class, they should grow up with an intuitive idea of what mass is, and weight should be a weird scientific concept discussing relations of gravitational fields, which are caused by mass.
Maybe once we colonise other planets we'll switch. But I doubt it. Few would hesitate to say the Sun rose this morning, after all.