Variations:

The number of cards dealt can be varied according to the skill levels of the players.
To simplify the target number to be reached, children could be allowed to use the two top cards in any order to set the target.
To assist younger learners, a set of operation cards will help.
The sets of playing and operation cards can be laid out and this will also help youngsters see that can only use each number once.
For children unable to mentally calculate the answers, paper and pencils should be available.