Estimation Guesstamation

The 1st grade teacher held up a 1" by 1" (approx) linking cube in front of her class. She told her students that they were going to be measuring some things in the classroom. They got very excited. They were going to use the blocks to measure things - including the height of someone in their group. The excited chatter began.
"Lets start by estimating what Tommy's height is using cubes." Silence
"How tall do you think Tommy is?" Silence
"How many cubes do you think it will take to go from his toes to the top of his head?"

One student pipes up, "You mean like a guess?"
The teacher smiled. "Yes! A best guess."

Estimation
What are we really asking students to do with estimation? Are there different types of estimation that are used in different scenarios?

A primary student may think "best guess" is a random guess based only on an immediate number that comes to mind. When we begin to use strategies to make accurate estimations, students come up with amazing ideas.

• Put ten together and see about how many sticks of ten it will take
• Pretend you are holding a cube between your fingers and "walk" your hands up the side of the person
• Divide the person into "sections" and figure out how many tall the head, the leg, the arm is.

Why should we have students estimate? 

Primary students are still working on the idea of quantity, or the "largeness" of a number. More experiences with quantity will help them understand the magnitude of numbers. So, going back to compare their original estimate with the exact amount helps with this. 

Our elementary students often use estimation for reasonableness. The answer to 589 + 204 should be about 800.

A great resource for getting students to practice estimating is   ESTIMATION 180   This site has 180 days worth of quick estimating activities with pics.

So how many cubes would it take to measure the height of an average 1st grader? (About 60)