Grade 4 students need to be able to convert halves and fifths to decimal equivalents. This is done using materials as well as abstractly.
A good investigation is to give groups of students one of these fractions:
They shade that fraction of a tenths grid in, and use this representation to convert fraction to tenths, then a decimal. For example, two fifths is shaded in:
and the visual used to convert the lowest term fraction to 4 tenths.