Mathematics skills can improve with just one technique -practice! Most of the children end up petrified of numbers and number games because of lack of appropriate knowledge. All this is a result of poor teaching mechanics. The vast school curriculum does not teach the children the perfect way of learning the subject. It is only proper practice and regularity that can make a student reach perfection.
There are many kinds of worksheets available but the best one is still the personally drafted one. This way one can easily check the level of difficulty that is offered to the kids according to their age and even check the progress level. Worksheets can be reused but it is always better to upgrade them from time to time.