Science makes the assumption that the natural world can be understood by using evidence from the natural world.  Scientists create explanations for natural phenomena by interpreting evidence.  The stronger the supporting evidence, the better the explanation!

According to the U.S. National Research Council, the following five features are at the core of teaching through science inquiry:

  1. Learners are engaged by scientifically oriented questions.
  2. Learners give priority to evidence, which allows them to develop and evaluate explanations that address scientifically oriented questions.
  3. Learners formulate explanations from evidence to address scientifically oriented questions.
  4. Learners evaluate their explanations in light of alternative explanations, particularly those reflecting scientific understanding.
  5. Learners communicate and justify their proposed explanations.

At the core of this, is the creation of evidence-based explanations. These explanations should go beyond a simple conclusion that reports data. Students need to be given frequent opportunities to create evidence-based explanations and evaluate explanations to determine if they are supported by evidence.

The following mini case study is an example of how you can focus students on creating evidence-based explanations.  The case study is Inspired by the Student Self-Test for Chapter 1 of Oxford Big Ideas Science  (ISBN 978 0 19 556715 1, Oxford University Press Australia).

Explanations, Evidence, and Cane Toads

An average cane toad can grow to the size of a softball. Adults have poison glands located behind their eyes and tadpoles are highly poisonous to most animals. Females will lay thousands of eggs. Cane toads have a huge appetite and, unlike most toads, will eat both living and dead matter. Cane toads can recognize their food by smell, but most often identifies prey through motion.  Cane toads’ main diets consists of insects, but they also eat small rodents, amphibians, reptiles, small birds, plants, dog food, and household trash.

The cane toad gets its name because it was commonly used to eliminate pests in sugar cane fields.  Although it is originally from Central America and northern parts of South America, the toad was used in the 1800’s and early 1900’s throughout the Carribean and Australia as a way to control beetles and other pests ravaging farmers’ fields.  Since the skin of adult toads are poisonous to many predators in these areas, they are now considered invasive species.

A Sydney University professor and his student, studying captive cane toads, noticed that they exhibited cannibalistic tendencies.  They observed adults wiggling their toes when around young toads. When the young toads hopped towards them, the adults would eat the youth!  Based on these observations, the scientists developed a laboratory investigation. Adult and young toads were separated by clear glass so they could not eat each other (ethical investigation). They observed that the young toads only approached adult toads that wiggled the middle toe on their hind feet.

Task: There is a lot of information (data) in these three paragraphs.  Scientists go beyond simply reporting observations by creating evidence-based explanations for what they are seeing.

  1. Summarize the important data from the text.
  2. Write an explanation that explains they scientists’ observations.  Make sure you support your explanation with evidence from your data in #1.  Go beyond a simple reporting!