These two worksheets look at doubling larger numbers, including those in the teens. It is well worthwhile asking children how they have worked these out in their heads, making use of the knowledge they have. For example doubling 17 can be worked out in several ways:
double 10 and double 7 and add
double 7 and double 10 and add
double 20 and take 6 away
double 15 and add 4.
Children will develop different methods but they do need to be shown that there is more than one way to reach the answer. The ultimate aim is to find a variety of efficient quick methods for calculating.