On the surface it appears that most of this task was not difficult. However, an analysis of the data from the trials shows two areas of difficulty: Features of the animals and classifying animals.

1. Features of the animals

Many students had a poor knowledge of the features of the various animals. The most frequent mistakes were related to backbones and blood temperature. Neither of these features can be observed from the pictures, but are important for classification.

Snake: 114 students thought that a snake has gills, and 35 that it is warm-blooded. Research has shown that a common misconception is that snakes have no backbone. This was confirmed by our trial – 79 students made this response.
Moray eel: 48 thought it did not have a backbone.
Dolphin: 69 said a dolphin has gills, and 64 that it is cold-blooded.
Goldfish: 37 thought a goldfish has no backbone.

2. Classifying animals

Although students were usually able to classify the animals correctly, they did not always use the information they had gathered to decide whether or not the animals were fish. For example, they generally were able to identify most of the moray eel's features, but 63 did not classify it as a fish. This may be because so many of them incorrectly stated that it had no backbone.

79 students classified the dolphin as a fish.

Probing for understanding

Teachers could ask questions to check if students are:

• referring back to the information in the box about classifying fish;
• able to retain that information while they are completing the task (research into comprehension skills has identified that many students do not retain information read in the previous paragraphs);
• using other irrelevant criteria, such as living in water;
• using just one of the criteria to make decisions.