kitchen table math, the sequel: Obi-Wan on calculators

Sunday, July 12, 2009

Obi-Wan on calculators

It bugs the hell out of my kids, but I love saying it:

The fact that you're asking for a calculator is the surest sign that you shouldn't have one.

I have seen far too many kids so clueless about basic computations that they can't even recognize an answer which is off by several orders of magnitude. They add two numbers and get a smaller number. No clue.

I don't do mental math well at all. I was never taught, and when I taught myself how to do it in order to teach my little afterschool Singapore Math class, I didn't practice it enough to learn it well. (I think Saxon Math has some mental math exercises, right? Or am I confusing the two curricula?)

Now that I know a bit about it, I'm a big fan of mental math.

math dunces


MiaZagora said...

Saxon does have mental math exercises before each lesson.

Anonymous said...

Saxon does have mental math for about 15 minutes before every lesson. I remember skipping them with my special ed son for a while. When I realized that I was probably making a mistake, I was amazed at the difference they made in his speed and even understanding.

Saxon tends to use the mental math section to support the upcoming chapter, which is quite helpful.


Catherine Johnson said...

I thought so!

We did everything (I took C. through every lesson in Saxon Math 6/5) - but I just couldn't remember specifically whether we'd done mental math exercises.

ChemProf said...

Oh, mental math is so important! I can't tell you how many of my students reach for their calculators when I ask them to do something simple like multiply by 10 or figure out 10% of something. It is really just a matter of habit -- they reach for the calculator before they even think about what I asked!

Barry Garelick said...

And interestingly, Investigations and EM both boast about how their programs emphasize mental math. Though they don't seem receptive to the idea of teaching long division. I wonder why not? Long division is an ideal way to hone mental math skills. A problem like 56,098 divided by 84 requires a lot in the way of number sense and mental math. The first step is looking at the maximum number you can have to multiply by 84 and stay under 560. Rounding, 560 divided by 80 would be 7, but a quick glance will tell you that 7 x 84 will be greater than 560, which quickly leads you to "6" for a choice. And so on and so forth. But reformers don't want to hear about all that. It's drill and kill, has no value, and anyway, calculators have made long division obsolete.

Catherine Johnson said...


All of the mental math practice I got as a kid was in long division.

K9Sasha said...

When I started homeschooling my son in 9th grade he hadn't yet memorized his multiplication tables (that, plus the fact he couldn't write his way out of a paper bag, were the two big reasons I started homeschooling him). I used the Otter Creek program* and he learned all his addition and multiplication facts.

In tenth grade he took the PSAT test and the first thing he said to me after the test was, "Thank you for making me learn my facts. The first question on the math section was a simple 2x=(something) problem and by the time everyone else had their calculators out, I was done with it." I loved that comment!

*The Otter Creek program has students work with just two new facts at a time. They take a one minute time test daily until they can answer all 40 problems in one minute, then they move up to the next level which includes everything they've practiced so far plus two new facts. I like that there are only two new facts at a time and lots and lots of opportunity for practice and consolidation.

CassyT said...

Two items - first, I like the FAN-Math MathExpress series for speed math strategies - Levels 3-5 are good.

Second - At a charity silent auction last week, we had won 3 items. The winning bids were: $15, $ 27, $25. My son (13, going into Geometry) said: "That's $67", because the adult was having trouble adding the numbers. She said, "Well, we better check and make sure you're correct."

And a few minutes later she confirmed that he was.