PESTL Science Investigations
Science investigations are not all created equal. What is the difference between a science experiment and a descriptive investigation?
Science experiments are investigations that scientists use to change a variable to determine the effect on other variables. The classic example is “What is the affect of light color on plant growth?” In this experiment, the variable color of light is changed by the student. The student may compare red light to green light. The thing the scientist modifies is identified as the “Independent Variable.” Another classic example is “What is the affect of refrigeration on popcorn popping?” In this experiment, students pop popcorn that has been refrigerated compared to popcorn that has been left out in a warm dry place for a number of days.
In each of these investigations it is important to keep the other variables constant. It would not be a fair test if the plants under the green light received a different amount of water or if the popcorn in the refrigerator was a different brand. The things in an experiment that are kept the same are identified at the “controlled variables.” Students are keen to identify the things that make an investigation fair.
In the investigation the things that change, amount of plant growth or number of kernels that pop are identified as the “dependent variable.” It is important for students to make the link between the independent variable and the dependent variable in the results.
It is important in any investigation for students to make warranted inferences. Making warranted inferences and conclusions mean limiting the findings to the investigation that is done and avoiding unsubstantiated claims.
Teachers should use language and expect language from students such as:
· The evidence from this investigation indicates that plants tend to grow better under the green light than the red light we used in our investigation.
· This investigation leads us to conclude that plants grow taller under green light than red light.
· We have evidence to support our hypothesis that plants grow better under green light than red light.
Teachers should try to keep students from using conclusions like:
· We proved that green light is better for plants
· We conclude that all plants grow better under green light
· Green lights increase the rate of plant growth by increasing photosynthesis.
Not all investigations are experiments. Much of science is conducted with investigations using observations that result in descriptive findings. Astronomers, meteorologists, and geologists do science through descriptive investigations. Classification of leaves is an example of a descriptive investigation. Identification of patterns in clouds and weather is another example. Descriptive investigations use careful observations and measurements to develop findings. Student science journals, science logs, and field notebooks are some of the tools students can use to gather information for descriptive investigations. The ways students organize this data and warranted inferences provides for powerful science learning opportunities.
It is important in these descriptive investigations for students to make warranted inferences.
Teachers should use language and expect language from students such as:
· In the observations made on the patterns of the moon in the sky at 9pm during the first two weeks in September, we found that the moon appeared in the sky to be further to the East.
· We collected leaves from five trees. Two of the trees appear to be closely related since the structure of the leaves had very similar patterns.
· Using the Peterson Field Guide for Identification of Birds, we identified three distinct species of birds observed at our school bird feeder during the month of January; 1) Slate-sided Juncos, 2) a group of finches that appeared to be either the House Finch or the Cassin’s Finch and 3) Cedar Wax Wings. The Field Guide provided information that indicated that the Cedar Wax Wings are not as common for our area as the other two species.
Teachers should try to keep students from using conclusions like:
· We proved that Juncos are the most common winter bird in Utah.
· All of the leaves we found were Red Maples because most trees belong to the maple family.
· All, never, always…etc.
Connecting the investigations to information gathered from reliable sources such as reputable books, valid online sources, and journals enhances the learning experience. Field guides are very accessible sources of information for students. Students should value their own science findings and use resources to add to the clarity of their findings. It is important the students write their findings in statements that they can defend with evidence. Writing using evidence to support assertions is one of the most powerful tools students can gain. Science is a way of knowing that relies on empirical evidence. When students write using their own findings they are able to formulate arguments that are based on science findings. Teachers who use a “Talk and Argument” approach to classroom discussions find that their students transfer this approach to thinking into their writing.
Regardless of the format of the science investigation, it is important the instruction includes clear understanding of the processes of science, nature of science, and the content. Using words carefully is a trait of good science. Teachers should be cognizant of distinguishing between various types of science investigations. Students understanding the nature of science may be of the most important way to begin developing science habits of the mind. Finally, the most important science goal of instruction at the elementary grades is that teaching and learning science is enjoyable and sparks student curiosity.