clockwise

We are fans of any method that encourages numeracy and engages and like the concept behind the Albert Clock, which does not surrender the hour without a challenge.  I always liked doing factorials (n!) myself and working out how many ways and with what operators one can reach a given number.  Depending on your target audience—this would be a good addition for a classroom or waiting area, the skill level of the problems to solve can be dialled up or down.