Still, I occasionally see things in the Common Core math standards (CCSSM) that make me stop and wonder, "How are teachers going to deal with this?" One recent instance of that was with how the CCSSM addresses the topic of absolute value. As I looked through Discovering Algebra: An Investigative Approach, I saw the typical "distance from zero" definition followed by an investigation that included this rather unhelpful picture and caption:
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| (Clearly portrays Elvis? The middle guy looks like Matthew Perry joined a Vegas lion-taming act.) |
From there, Discovering Algebra presents students with equations to solve, such as:
$$ | x - 2| + 7 = 12 $$
But do the CCSSM call for solving these kinds of equations? I went searching through the CCSSM for all mentions I could find of absolute value, and here's what I found.
Grade 6
CCSS.Math.Content.6.NS.C.7 Understand ordering and absolute value of rational numbers.
CCSS.Math.Content.6.NS.C.7a Interpret statements of inequality as statements about the relative position of two numbers on a number line diagram. For example, interpret –3 > –7 as a statement that –3 is located to the right of –7 on a number line oriented from left to right.
CCSS.Math.Content.6.NS.C.7b Write, interpret, and explain statements of order for rational numbers in real-world contexts. For example, write –3 oC > –7 oC to express the fact that –3oC is warmer than –7 oC.
CCSS.Math.Content.6.NS.C.7c Understand the absolute value of a rational number as its distance from 0 on the number line; interpret absolute value as magnitude for a positive or negative quantity in a real-world situation. For example, for an account balance of –30 dollars, write |–30| = 30 to describe the size of the debt in dollars.
CCSS.Math.Content.6.NS.C.7d Distinguish comparisons of absolute value from statements about order. For example, recognize that an account balance less than –30 dollars represents a debt greater than 30 dollars.
CCSS.Math.Content.6.NS.C.8 Solve real-world and mathematical problems by graphing points in all four quadrants of the coordinate plane. Include use of coordinates and absolute value to find distances between points with the same first coordinate or the same second coordinate.
and
CCSS.Math.Content.6.SP.B.5c Giving quantitative measures of center (median and/or mean) and variability (interquartile range and/or mean absolute deviation), as well as describing any overall pattern and any striking deviations from the overall pattern with reference to the context in which the data were gathered.
If all goes according to plan, there shouldn't be a need to define absolute value in 8th or 9th grade algebra, as it will already have been introduced in 6th grade. I know there are concerns about content being "developmentally inappropriate" for lower grade levels in the CCSSM, but without any personal data to the contrary, I imagine students could come to understand absolute value along with understanding positive and negative numbers. The last standard above, from the moment I first saw it, has been a point of fascination for me. How will 6th grade teachers help students learn topics like interquartile range and mean absolute deviation? You need absolute value for mean absolute deviation, but I don't think that will be the hangup for those who struggle with that standard.
So where else is absolute value mentioned?
Grade 7
CCSS.Math.Content.7.NS.A.1c Understand subtraction of rational numbers as adding the additive inverse, p – q = p + (–q). Show that the distance between two rational numbers on the number line is the absolute value of their difference, and apply this principle in real-world contexts.
and
CCSS.Math.Content.7.SP.B.3 Informally assess the degree of visual overlap of two numerical data distributions with similar variabilities, measuring the difference between the centers by expressing it as a multiple of a measure of variability. For example, the mean height of players on the basketball team is 10 cm greater than the mean height of players on the soccer team, about twice the variability (mean absolute deviation) on either team; on a dot plot, the separation between the two distributions of heights is noticeable.
Now we have absolute value as it relates to subtraction, and we get another mention of mean absolute deviation in the 7th grade statistics and probability standards. There's nothing yet about solving equations with absolute value or graphing absolute value functions.
Grade 8
Nothing. No mention of absolute value or mean absolute deviation.
High School
The CCSSM doesn't specify what specifically belongs in 9th grade versus other grades, but here's what I found across the whole of the HS CCSSM standards.
CCSS.Math.Content.HSN-VM.C.12 (+) Work with 2 × 2 matrices as a transformations of the plane, and interpret the absolute value of the determinant in terms of area.
CCSS.Math.Content.HSA-REI.D.11 Explain why the x-coordinates of the points where the graphs of the equations y = f(x) and y = g(x) intersect are the solutions of the equation f(x) = g(x); find the solutions approximately, e.g., using technology to graph the functions, make tables of values, or find successive approximations. Include cases where f(x) and/or g(x) are linear, polynomial, rational, absolute value, exponential, and logarithmic functions.
CCSS.Math.Content.HSF-IF.C.7b Graph square root, cube root, and piecewise-defined functions, including step functions and absolute value functions.
The first of the three standards above, I think we can agree, goes well beyond what we'd expect to find in a traditional Algebra 1 class. The other two standards address the graphing of various kinds of functions, and depending on the activity might belong in either a traditional Algebra 1 or Algebra 2 course, or more likely, both. But do you notice what's not there? Solving equations with absolute value functions. Sorry, \( | x - 2 | + 7 = 12 \), but it looks like you didn't get invited to the CCSSM party. Even if you interpret the second standard to include solving absolute value equations, it only asks for an approximation or to use technology.
Conundrum
The researcher in me wonders what Algebra 1 teachers will do when they get to a lesson on absolute value. Will some just teach it out of habit? Will some think it was excluded due to a CCSSM oversight? Will some modify the lesson to emphasize the graphing of absolute value, but not solving absolute value equations? How many will not even notice it went missing from the standards? Will anyone be willing to kill the little darling?For years we've lamented math curricula in the United States that was "a mile wide and an inch deep." Given a fixed amount of time, going deeper means going narrower, and there is evidence that the CCSSM supports that (Porter, McMaken, Hwang, & Yang, 2011). For reasons I perceive to be mostly political, the Common Core State Standards don't go out of their way to specifically address content omitted compared to previous standards documents. In 1989, NCTM made a list of areas of emphasis and de-emphasis and many an argument in the math wars was waged using false dichotomies rooted in those lists. I'm sure those who wrote the CCSSM didn't want a repeat of those arguments, so now math teachers and those who support them are left to dig through the standards and find these omissions on their own.
(By the way, if you're looking for an interesting lesson for understanding and graphing absolute value, NCTM is offering one from a recent Mathematics Teacher for complimentary download: Angela Wade's "Teaching Absolute Value Meaningfully.")
References
Porter, A. C., McMaken, J., Hwang, J., & Yang, R. (2011). Common Core standards: The new U.S. intended curriculum. Educational Researcher, 40(3), 103–116. doi:10.3102/0013189X11405038