In order to engage a reluctant worker, King of Math is an app I’d highly recommend.
The app appears more like a game, as children can collect medals and complete levels to progress.
Children start off as a farmer and are tasked with answering 10 addition or subtraction questions simply by selecting the correct answer from 4 different options. The longer it takes to answer these questions, the more their overall score drops (what is left over adds onto their overall score at the end of each level) and their rating declines, providing them with an incentive to work quickly and correctly.
If you purchase the full version, for a one-off payment of £1.49, children can also study multiplication, division, arithmetic, geometry, fractions, powers, statistics and equations as well.
As the children progress through the levels they can progress their character from a farmer to a king, which will help engage even the most reluctant learner as they have a fun goal to reach.