We have been using the metric system to measure mass (weight) with a balance beam. And we have learned that the basic unit used to measure weight is the gram, that 1,000 grams make a kilogram and that we use the kilogram to measure the weight of larger objects. The students have gotten pretty good at estimating the weight of familiar classroom objects, in grams.
Now we are turning our attention to measuring volume. If you have some clean, dry containers that that your student can bring in, it will help us continue our investigations into this "spacey" thing called volume. Your student just might be able to tell you what those other (metric) numbers are on the stuff you buy at the store!