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Here's a mnemonic aid for teaching how to move the decimal point in the correct direction when multiplying or dividing by powers of ten (ie. ten, or a hundred, a thousand etc.), sent in (9/00) by Barbara D. Martin:

divide • multiply d - e f g h i j k l - m i go left i go right

Some students can have trouble remembering which way to move the decimal point, when multiplying or dividing a number by a multiple of 10. Show them when dividing, that just as the letter "d" is to the left of the alphabet so they should move the decimal point to the left. Likewise when multiplying, they should move the decimal point to the right just as the letter "m" is closer to the right of the alphabet. Thus for example:

When teaching this to young children, you might add that "you and i go left.." or "you and i go right.." starting from little i (the letter with the decimal point on top!) - though don't tell the English teacher or you'll get into trouble for not using a proper capital I !