This Is What Common Core Looks Like

First of all parents were not able to help their children with old methods either. Give someone a pen and paper and ask them how to add 17% to 58. You don't want an answer - just a working method. A lot of people can't do this on paper, but that's okay because we have computers to do that stuff. Lots of people can't add 17% to 58 using a computer. I find that a bit scary.

Going on to the example: I'm pretty stupid; I've often said that I am hopeless at math. I found that single example really easy to understand. I've not had any exposure to similar examples. I don't believe the author is actually baffled by the example. Perhaps a book might help?

http://www.robeastaway.com/books/maths-for-mums-and-dads

> What on earth are number bonds? What are partitioning and chunking? And why does my child look blank - or have a tantrum - when I demonstrate long multiplication? This book is for mums, dads and grandparents who want to help their primary school children or grandchildren with maths. To do so, many parents find they need to overcome their own rustiness and also to learn the strange new methods and terminology. Throughout the book are games, puzzles and examples of amusing ways in which kids ingeniously 'get it wrong'.

That problem is the false belief that numeracy is improved by learning different ways of looking at number operations. (i.e. four ways to subtract).

Our child's second-grade teacher (a very good teacher) has a poster illustrating 7 ways to subtract. Seven ways, no exaggeration. This poster is older than common core.

Students learn math just like they learn to kick a ball. By practicing. Learn one way to subtract, and practice it really really well. Or learn two ways, and practice each way really, really well. Learn more ways if you want, but practice each way really really well. Most math curriculums assume that learning multiple ways is equivalent to (or better than) practicing one way. They don't require the repetitive practice.

As comments have pointed out, the common core standards don't explicitly require this multi-way approach. But the CC standards compound the problem by requiring students to explain concepts in order to demonstrate mastery. Completing lots of subtraction problems with a low rate of error doesn't count. You must explain, in order to understand. And if you really understand, shouldn't you be able to explain different approaches?

I would say no. Or at least, not yet. I don't want a third-grader explaining how to subtract unless they can also finish 50 subtraction problems in a row without pausing to struggle. And if they get the problems right? Good job, you get an A. Wonderful, let's skip grading the explanation because that is subjective as hell.

TL/DR: The article rightly points out a crap way to teach math. Common core is not totally to blame, but it makes a bad problem worse.

I use something similar to avoid getting too much change at a cashier, and to use up loose change (pennies, nickels, etc), except I usually count down and add in the difference. So, for example, if some bubble gum cost $1.28, I might give the cashier $2.03. Then, assuming the bewildered cashier doesn't try to give me the pennies back, I get three quarters for laundry, instead of two quarters, two dimes, and two pennies.

If I don't need laundry change, I'll count up or down searching for the amount that will maximally reduce the number of coins in my pocket (without avoiding bills, which would just be annoying to everybody). With practice you can do this in a split second, and it really blows the mind of some cashiers.

Isaac Asimov said something to the effect that smart people will tend to figure out these algorithms on their own. So it's kind of ironic that now somebody is complaining that it's being taught to kids. I suppose the only real legitimate criticism here is that, according to the link, there's only one example of this method, and then it's never mentioned again. If anything, it should be expounded upon.

There's no strong reason to glorify one particular subtraction algorithm over another, especially since the actual use case for it is relatively rare.