Erika Isomura teaches fourth and fifth grade at Glassbrook Elementary in Hayward, California; 22 of her 30 students are fifth graders. Depending on the content and her formative assessment of her students, at times she groups her 4th and 5th graders together for mathematics lessons and at times she differentiates with mixed groups. She also documented a lesson [earlier in the year](http://www.insidemathematics.org/classroom-videos/public-lessons/5th-gr…) focused on representing fractions.
In this lesson segment, recorded over two days one week apart, Erika builds on this prior work with fractions and develops her students’ ability to “use calculators using a new type of number called decimals,” so that they can find “another way to say eight hundredths, or eight thousandths, or so on.”
This approach differs from traditional methods of teaching decimals as rules — e.g., “how many zeros do you add?”
Erika’s approach develops her students’ understanding of magnitude and number sense: roughly how much should that be? What does that look like?
She also builds her students’ capacity to communicate precisely, “Dividends have 1 less zero each time. ‘Divisors’ is always 10...not just, ‘It's getting bigger or it's getting smaller,’ but really how is it getting bigger and how is it getting smaller.”
Her overall question addresses the root of the term “decimals”: that means 10, so how are 10s important in the way we build numbers?
This lesson, created by teacher Erika Isomura and coach Mia Buljan, was inspired by the [Georgia Department of Education’s 5th-grade “Patterns R Us” lesson](https://www.georgiastandards.org/Georgia-Standards/Frameworks/5th-Math-…).