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Bigger Number First

When my son was in the first grade he came home with some basic subtraction facts.  He created some of his own problems for practice (with my urging) and wrote 3 – 5.  I pointed out the problem to him and he said, “Oh yeah, I forgot, the bigger number always comes first in subtraction.”  I cringed.  I asked him how he knew that and he responded with that is what his teacher told him.  I’m not sure if it is a blessing or a curse to have a math teacher as a mom.

I explained to my son that you could in fact do subtraction with the smaller number first.  I explained the concept with money and owing someone money.  He quickly caught on to the idea of negative numbers and I introduced him to the correct terminology.  Of course, I think my son is brilliant, but I’m sure given a chance most young children could catch onto the idea. 

I overheard my son explain negative numbers to his younger brother yesterday.  My older son is now in 4th grade and my youngest is in kindergarten.  My youngest son seemed to get it.  If my kids can get negative numbers, why not introduce them earlier?  If teachers decide not to introduce them, that is fine, but don’t teach young children wrong rules like:  The bigger number always goes first in subtraction.

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Categories: Uncategorized
  1. Craig
    November 5, 2010 at 1:42 am

    The same can be said about division. “The bigger number always goes under the division sign.” Ack.

  2. November 5, 2010 at 2:09 am

    It’s alarming how that sort of thing sticks with them.

    “Two divided by five? That’s not a number!!!” -overheard in my Trig class just yesterday

  3. November 5, 2010 at 4:45 am

    @Kate I got that today. “That’s impossible!”

  4. November 5, 2010 at 1:37 pm

    I also have to unteach that you have to change improper fractions to mixed numbers. Argh! I’m a big fan of certified math coaches in the lower grades for this reason.

    • November 5, 2010 at 2:28 pm

      I agree. I cringed when I saw that in “Teach Like a Champion” (P. 91, “When a student in her fifth-grade math class was unable to explain what was wrong when writing the number 15/6, …). In fact, it made me put the book away for several days, and lowered my opinion of Lemov by several notches. I almost didn’t pick the book up again.

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