The process of estimating in Kindergarten is still in the beginning stages.
In later grades, students have more operational sense that they use in their estimates. Students use a referent – a known quantity – to extrapolate to the whole quantity being estimated. In Kindergarten, they usually lack the beginnings of proportional reasoning this requires.
A grade 2 student might think:
|This is about 10|
|So this pile is about 10, 20, 30, 40, 50, 60, 70|
In FDK, they tend to use an overall sense of quantity – it’s about 8, or about 5, depending on their number knowledge. You can see students who when shown 10 cubes then estimate a pile several times larger as 14, or even 11. Many students are still thinking in terms of relative magnitude and choose a number they just know is larger.
When students start to unitize and can skip count, connecting this skip counting to quantity and not just the number sequence, their estimation becomes more accurate.