Take, for instance, this current british road sign indicating the steepness of a hill:
Why is it, that although we have a statutory national curriculum in which everyone learns that gradients are given as single figure ratios of 'rise / run', this road sign flies in the face of that fact and gives the steepness as a percentage? A percentage is an appalling way to measure steepness. It is not immediately clear whether this sign would indicate a slope with a gradient of 0.1 or a slope at an angle of 10% of a right angle. Either way, it is a disconnect from the idea of gradient as it is learned in school.
Gambling odds are another example of classroom maths being mismatched from 'real-world' maths. (Of course, I am obliged here to say that I am not advocating that we should encourage students to gamble by teaching them about it. However, avoiding the topic in the classroom is not helping students to make informed choices about it later.) Again, following the national curriculum, probability is developed as a single number proportion - in this case, interchangeably fractions, decimals or (less frequently) percentages. When encountering betting odds in the real world, we are faced with a pair of numbers to interpret:
Differences like these serve to fuel the notion that the language of classroom maths is not the same as the language of real-world maths. To students who are already inclined to think they cannot do maths, this surely reinforces the idea in their mind. If we really want to educate students to be pragmatically numerate in the 'real world', educating students in a different 'language' will not help!