A Glass Half Full

Today I was conversing with a friend about the size of the glasses we have. She was wondering if her glasses were bigger than ours and we were musing that because of the fluting on our glasses if you filled them to half the way up you probably wouldn't get very much drink. We wondered where the "half way" mark would be on our glasses if you were judging by volume.

I figured the kids could help us find out where "half a glass" actually WAS on our glasses. I think easiest way to get my kids interested in doing scientific experiments is to show them how I do it, so we played a game with it. I got a permanent marker and got the kids to each have a guess where "half way" was on a glass. It's through discussing things like this that you really begin to get an idea of things like "volume", "size", "halves", and the conventional language and meaning of measurement. The kids have heard that liquid is measured in litres or millilitres (or mls). It is something that they will grow familiar with over time, but not something I need to push. Once they have experience with measuring liquid, for experiments, or cooking, or craft, or buying liquids, filling bottles... then words like cups, litres and millilitres will just be normal, and they will have constructed their own understanding of how much those measures are.

I filled the cup all the way to the brim, and then poured that liquid into a measuring jug. It was exactly 300ml. I asked my son(7) how much half of 300ml would be, and he didn't know. I counted the divisions of 50ml on the jug. There were 6, so I asked him half of 6, which he got, and we counted up 3 and found 150ml.

Then the moment of truth... pouring the water back into the glass. "I got pretty close!" he cheered. This is fantastic for him, because he's finally aiming for a best guess rather than perfection. He's come so far. I'm happy for him.

This is such a cool way of doing things because the results are self evident and he gets to assess for himself how well he is doing. He gets to feel successful and know his own merits without it being anything to do with my approval of him. My judgement or ideas of him are not necessary when he can assess for himself how well he is going, and when he is the one setting his success criteria he doesn't feel crushed when it doesn't work out. He's not disappointing me, or facing my criticism; it's a low risk activity.

And yep... our glasses are half full at about two-thirds of the way up the glass!