Many children love snow. If your science lesson coincides with a snowfall, get your students to investigate whether any two snowflakes are the same. Be prepared by having some black card or black felt in the freezer. Use this to catch some flakes of snow and then examine them with a magnifying glass or the Science Year digital microscope (www.planet-science.com) Flakes melt quite quickly, but the frozen material should give you enough time to view them. You could photograph some snowflakes through the microscope, or get some images from the web. One great source of images is www.its.caltech. eduatomicsnowcrystals where a method of catching a snowflake image with glue is described. Encourage the class to spot any similarities in the snowflakes - for example, they are all six-sided and usually symmetrical. The symmetry is due to the arrangement of water molecules and lack of symmetry is usually caused by the presence of dirt, or uneven environmental conditions during the snowflake's development.
You can make your own "snowflake" by crystallising borax. Take a wide-mouthed glass jar. Twist pipe-cleaners into a six-sided snowflake shape and suspend it in the jar from a pencil to check it fits. Remove the snowflake and fill the jar two thirds full with warm water. Add three or four tablespoons of borax and stir until dissolved.
Now replace your snowflake and leave it for at least 24 hours. When you return, it should be really sparkly as the borax has crystallised on to the pipe cleaner.
Remember borax is a strong detergent. Handle the snowflake with plastic gloves or from the suspended string. If you do touch it, wash your hands.
Sophie Duncan is project manager for science at the BBCwww.bbc.co.ukscience