*This is Day 18 of the 30-day blogging challenge, for anyone still keeping track. Like me. Or my students who want to see if I make it.*

Once upon a time, I used to teach a subject called *Math A*. It was something that the state decided should be taught to freshmen and sophomores in high school instead of the inferior (I'm just inferring from the switch) *Sequential I*. Sequential I, which would be followed by II and III, just as Math A would be followed by Math B, was something that came long after I got out of high school -- I had *Math 9*, in eighth grade, for that matter -- and disappeared by the time I became a teacher. Math A eventually gave way to the far superior *Integrated Algebra*, which I say lovingly, and yet mockingly, because it's all essentially *the same math*! Little tweaks here and there (e.g., *relative error* instead of *percent of error*) and switching the order of the topics and the maker of the textbooks, but essentially the same.

Through it all, when it came to scatter plots, we showed them how to make a line of best fit. All we ever seemed to care about was if the line that they drew was "reasonable". There wasn't a "right" answer which we were expecting because that was something that was a little beyond them. Sometimes, we had them come up with the equation of the line of best fit, but this confused many because they had different lines, so they had different answers. Still, it was a good exercise because it reminded them how to write the equation of a line from a pair of points. It also got them used to dealing with fractions, ant that is a whole different topic altogether! *("That is a whole different topic!" they repeated in unison)*

Along comes *Common Core* and someone realized that these kids are already using graphing calculators for their tests (which weren't allowed just a decade ago, but are now *required*), let's teach them how to use them. I'm all for that, except that the students never seem to have them. We can't require them to buy them (except, perhaps in specialized schools) and class sets have a habit of breaking and disappearing. When this happens, not everyone is learning how to use them and then no one can help them on test days. Now, this isn't a problem for most things -- after all, a lot of it is intuitive, and a lot of it is repeated often throughout the term, like graphing.

But then there's linear regression. That's one of the last things we teach. It doesn't get used again. I hope it's stuck in their brains instead of them stuck in the mud and left behind.

Today was the first time that I had to teach it to freshmen. I'm familiar with the process of using Lists (behind the STAT key) and calculating y=ax+b (with the use of *a* instead of *m*). That's all good. The forty-six bazillion decimals, instead of a more familiar 7/5, for example, get a discussion on proper rounding. But today was the first time that I ever had to teach about the *correlation coefficient*, which before now, I've really only seen in an Excel spreadsheet -- in my final grad school class. (Okay, I probably saw it sometime during a *Statistics* class in college, but I know that I didn't own a graphing calculator in those days. I was lucky to have a **Commodore 64** with a modem at home.

Nothing on the **CALC** menu gave me any hints as to where I could find it, but a quick look at the Internet told me that I had the power to find it all the time. It was there in front of me. I should have found it with my brain or felt it with my heart, but I had the courage to look it up online instead.

The answer I needed will *NOT* show up unless you go to the **CATALOG**, scroll down to the middle of the letter *"D"* and find **DiagnosticOff** and **DiagnosticOn**. There aren't any check marks, but the thing defaults to Off. I had to instruct my students, many of whom knew little about the CATALOG in general, how to turn this on and why. They wondered why it wasn't on my default. (Okay, they didn't actually say "default", but that's what they meant!) I can understand why it defaults to *radians* instead of *degrees*, but this makes no sense to me.

The take-away from all of this is when we collect all the calculators and reset their memory, we not only have to reset each and every single calculator to *Degree* mode, but we'll have to go to the Catalog to turn **DiagnosticOn**. Twice the pain for little gain because we don't even know if they'll answer the questions, or if they'll even remember today's rather abstract lesson.

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