The origin of PTs’ difficulties seems to be a lack of understanding of place value
units and the relationships between units. Strategies used by PTs illustrate that they made
comparisons using procedures learned in elementary school, such as appending zeros and treating the quantities like whole numbers, or converting each decimal to a fraction and
finding a common denominator that allowed the numerators to be compared as whole
numbers. Putt (1995) suggested that some PTs had difficulty understanding that 0.7 and
0.70 are equivalent. In particular, they seemed to struggle to interpret decimals as
composites of multiples of units. These difficulties shed light on PTs’ interpretation of
decimals.