More to the point: Because the authors don't know what kind of algebra 4th graders should learn, and how it differs from high school algebra. Under-educated authors.
The child who has already learned to calculate the area of a rectangle is ready to *abstract* such proceedings by creating and using a FORMULA for doing so ... perhaps LxW or BxA.. Likewise for 32+(9/5)C and other formulas about child's-life measurements.
The label, "algebraic expressions", was one bad mistake of the SMSG Algebra Committee. Introductory algebra is all about FORMULAS for functions ... I.e. for generating numeric values from numeric entries. That group did not know the difference between a formula (for producing something) and an equation. End result ... authors still thinking that the variable are the letters ... rather than what the letters represent ... the "L" and the "W", rather than the variable lengths and widths.
There are some kinds of algebra that K-6 children can learn ... to help them to learn arithmetic. But NOT the kind of algebra that is shown on that page.
- -------------------------------------------------- From: "Haim" <firstname.lastname@example.org> Sent: Tuesday, October 23, 2012 9:22 AM To: <email@example.com> Subject: Re: Why?
> Robert Hansen Posted: Oct 23, 2012 6:51 AM > >>Why is the attached page in a 4th grade math text? >>Teaching algebra in 4th grade IS NOT the path to algebra. >>Teaching arithmetic in 4th grade IS the path to algebra. > > Bob, > > If this is not a rhetorical question, I can tell you exactly why they do > this. It is so that people like Paul Tanner can prove to you how much > more more rigorous the modern American schools are. > > Haim > No representation without taxation.