Unit C
Unit Fractions
Partition unit fractions to create smaller unit fractions
Partitioning a unit fraction into smaller unit fractions (e.g., partitioning each fourth into thirds to create twelfths) supports student understanding of the relationship between the digit in the denominator and the size of the partition.
Background
A unit fraction is the base unit of any fraction and always has a numerator of 1; for example, 1⁄4, 1⁄15, 1⁄23 are all unit fractions. Every fraction can be decomposed into unit fractions. For example, 3⁄4 is 3 one-fourth units (so one-fourth is the unit fraction and we are thinking about 3 of them). Partitioning a model involves determining and creating a unit fraction.
Consider the fraction one and three-fourths. This number can be decomposed using a unit fraction.
One and three-fourths
Seven one-fourth units
One and two-fourths can be composed using a unit fraction.
A student may say, “One whole is the same as 4 one-fourth units. I added another 2 one-fourth units to the whole to obtain 6 one-fourth units. So I can see that 6 one-fourth units is equal to one and two-fourths.
Use of unit fractions supports a deeper understanding of quantity. Notice that in the student dialogue above, early understanding of equivalency is being developed, i.e., one and one-half is the same as six-fourths. Counting by naming the unit fractions helps students to see the parts of the fraction when composing and decomposing. Notice that both counting unit fractions and composing and decomposing fractions are pre-cursors to addition and subtraction. For example, composing 6 one-fourth units is the same as adding 6 one-fourth units together to make one and one-half.
Tasks
Additional Prompts
These tasks emerged out of the fraction research. Teachers may wish to use them as diagnostic or summative assessments, exit cards, number talk prompts, or additional practice questions. By considering both the specifics of the cell and student use of purposeful models, teachers can support students in acquiring a strong conceptual understanding.