6. Use variables to represent numbers and write expressions when solving a real-world or mathematical problem; understand that a variable can represent an unknown number, or, depending on the purpose at hand, any number in a specified set.

Puberty. It's a stinky, oily, filthy business. As it turns out, though, we all have to go through it. Everyone's been the victim of growing pains, embarrassing voice cracks, and finally realizing that you're the horrible smell in the locker room everyone's been complaining about. Ouch.

No one was born knowing to buy deodorant, and, just the same, no one was born knowing how to make use of variables and expressions when solving problems. It's something that needs to be learned and practiced, not unlike like your students' deodorant-applying skills. (And until they get the hang of it, we'd invest in an emergency bottle of Febreze if we were you.)

Basically, this standard's purpose is to make sure (1) that students know what the heck a variable is, (2) that students can use expressions and variables to solve real-world problems, and (3) that students know what types of numbers variables can represent given their contexts.

Hopefully, students have dealt with variables enough to knock (1) out of the park pretty quickly. And if not, then a quick recap and a few practice problems should do the trick.

As for (2), that'll definitely take some practice. The goal is for students to be able to use variables and expressions to represent unknown values and simple (read: one-step) equations to represent real-world situations. In other words, this part of the standard finishes off 6.EE.2a, ensuring students can translate any English into Algebrese. And as long as they practice assigning variables to values and interpreting the relationships between those values, it'll be an algebreeze. (We had to do it.)

Finally, (3) tells us that students should realize that some variables can only represent certain numbers. For instance, if we bought an unknown number of deodorant sticks d, students should reason that it won't make sense for d to take a non-whole number value. Buying negative of fractions of deodorant sticks don't make sense within the context we've set up; that is, the context limits the types of values our variable can take. As long as students never forget the connection between math and the real-world situation, they should be fine.

And as long as they never forget their deodorant sticks at home, we should be fine, too.