Exemplar 30 of the Science Guidelines for Teachers (Science Teacher Guidelines, Exemplar 30, p. 108) illustrates an approach to teaching the topic of floating and sinking at junior class level. Suggestions are given in this exemplar of how scientific skills such as observation, predicting and experimenting are included in the approach. This exemplar can be adapted for use with older class levels such as third and fourth. It may also be used as an approach to teaching children with special needs.
The Science Guidelines state that children will develop their ideas about why some things float and others sink as they encounter the topic floating and sinking at different class levels (spiral curriculum). It is noted that children in the junior and middle classes will discover through practical work that buoyancy depends on a combination of factors, such as what the material an object is made of, its shape and the liquid in which it is placed. (Science Teacher Guidelines, p. 13).
The Science Guidelines note that investigations will enable children to discover that a material that normally sinks can be made to float by forming it into a hollow shape. These Guidelines note that some children may develop their understanding of the concept of density but that more formal work in addressing this concept is more appropriate at post-primary level. (Science Teacher Guidelines, p. 13).
Some children will probably notice through observation of pictures or real situations that oil floats on water, that cream floats on milk and that a ship floats in water. For gifted children it may be appropriate to work through such observations so that children might be led to speculate on how the oil is different/less dense than water.
From their investigations children will notice that objects sink generally if they are heavy for their size and that they usually float if they are light for their size. They will also notice that different liquids which do not mix float at different levels. This is how we can see oil, water or other liquids as different layers in water. Children might draw conclusions from such observations but it is not a requirement at the level of third and fourth class that density per se be addressed.