Caitlin is in Year 5 and has recently been introduced to decimal
notation. She is treating the decimal part of the number as another
(whole) number. For example, the number after 4.9 (4 wholes and
9 parts) is 4.10 (4 wholes and 10 parts). If the predominant discussion
in the classroom is with decimals of equal length, her wrong belief
is not challenged, and may continue to secondary school. Whole number
thinking is one of the longer-is-larger misconceptions.