EIGHTH-GRADERS CAN DO EXPERIMENTS BUT STRUGGLE TO EXPLAIN THEIR RESULTS

Exemplifying the richness of the ICT assessment, the series of investigations included in “Bottling Honey” measured both science content and practice. In this task, students conducted simulated investigations of the effect of temperature on the flow of liquids, beginning with simple experiments and progressing to more complex ones. Based on the results shown below, students demonstrated the ability to design experiments and gather appropriate data, but had more difficulty when required to explain their findings.

• See how selected student groups performed on the five steps of this task.
• See scoring materials for this task.

• Part A: Investigating the flow rates of liquids

Step 1 – Students perform two simple experiments:

Students began this task by performing two simple experiments in order to respond to the following multiple-choice questions:
Question 1: Which liquid flows most slowly at 20 degree centigrade?

• Corn syrup
• Honey
• Water
• Olive oil

Question 2: Which liquid has the same flow rate at 30 degrees Celsius as water at 30 degrees?

• Olive oil
• Corn syrup
• Honey

The students were presented with an image of four test tubes containing four different liquids: corn syrup, honey, water, and olive oil. Suspended above each test tube was a metal ball. The temperature beneath each test tube could be set from 10 to 100 degrees Celsius. For the first experiment, students needed to set the temperature at 20 degrees Celsius. The students then had to click on the “Drop” button on the screen, causing the metal balls to drop into their respective test tubes. The time it took for each ball to drop to the bottom of its test tube was shown onscreen.

To conduct the second experiment, students clicked the “Reset” button on the screen and followed the same sequence of actions as they did for the first experiment. The only difference was that in the second experiment, the temperature of the liquids needed to be set at 30 degrees Celsius.

The results showed that 88 percent of the students answered both multiple-choice questions correctly. Just over half of all eighth graders (54 percent) answered both questions correctly and explained their answer to question 2, receiving a score of “Complete” or “Essential”. Forty-six percent of the students received a score of “Partial,” “Inadequate,” or “Incorrect.”

Try It Yourself: Users can perform the experiments using the animation presented onscreen.

Step 2 – Students design an investigation:

Next, students were confronted with a more difficult challenge. They were asked to design a multi-step investigation to explain how temperature affected the flow rates of the liquids. The task posed to the eighth-graders was, “Describe the steps you will take to investigate which liquids flow more quickly at a higher temperature than at a lower temperature.”

The eighth-graders were presented with an image of a single test tube over which was suspended a metal ball. For the experiment, students needed to select any one of four liquids—corn syrup, honey, water, or olive oil—to fill the test tube. They also needed to set the temperature beneath the test tube anywhere from 10 to 100 degrees Celsius. The students then had to click on the “Drop” button on the screen, causing the metal ball to drop into the test tube. An onscreen table recorded the type of liquid tested, the temperature selected, and the time it took for the ball to drop to the bottom of its test tube. Students could click on a “Reset” button, change the liquid in the test tube and its temperature, and perform the experiment as many times as they wished.
Results showed that 52 percent of eighth-graders could design a valid investigation. Responses received a score of “Complete” for providing three of the following components, and a score of “Essential” for providing two:

• Testing all four liquids
• Testing at a minimum of two different temperatures for each liquid
• Comparing the drop times of the balls in each liquid

Eighth-graders who were successful in answering the first two questions in Step 1 were more likely to design a valid investigation. Of the 54 percent of students whose answers to the first two questions were either “Complete” or “Essential,” 33 percent correctly designed a valid investigation. Of the 46 percent of students whose answers to the first two questions were “Partial,” “Inadequate,” or “Incorrect,” 18 percent designed a valid investigation.

Try It Yourself: Users can perform the experiment and view the data table using the animation presented onscreen.

Step 3 – Students interpret their data:

After the students implemented their investigation, they interpreted the collected data by answering the following question: Which liquid flows more quickly at a higher temperature than at a lower temperature? Select all that apply.

• Corn syrup
• Honey
• Water
• Olive oil

The students needed to review the results of the experiments they conducted in Step 2, which had been recorded for them automatically in an onscreen data table.

Results showed that 45% of eighth-graders selected at least two of the three correct liquids; 23 percent of the students were also able to support the correct selections with an accurate explanation. Twelve percent of all eighth-graders successfully completed all three steps of the task. Of the students whose answers to the first two questions in Step 1 were either “Complete” or “Essential” and who correctly designed a valid investigation, 12 percent received a score of “Complete” for their interpretation of the data from the experiment. Of the students whose answers to the first two questions were “Partial,” “Inadequate,” or “Incorrect,” but who were able to design a valid investigation, 4 percent received a score of “Complete” for their interpretation of the data from the experiment.

Try It Yourself: Users can perform the experiment, view the data table, and then draw conclusions using the animation presented onscreen.

Part B: Engaging in real life scenarios

Step 4 – Students explore the flow rate of honey:

In the final part of this task, students responded to two real world scenarios. The first was described as follows: A food processing company bottles honey. They want to bottle the honey as quickly as possible while using the least amount of energy to heat the honey. Now use the simulation to investigate the relationship between the temperature and the flow rate of honey over a range of temperatures. Which graph shown below best represents your results?
Students were to select one of four graphs. For each graph, the “x” axis represented temperature and the “y” axis represented flow rate.

• Graph 1 showed a horizontal line drawn from the midpoint of the “y” axis and running parallel to the “x” axis.
• Graph 2 showed a line beginning near the intersection of the “x” and “y” axes and steadily increasing upward from left to right.
• Graph 3 showed a line beginning near the top of the “y” axis and steadily decreasing downward from left to right, ending just above the “x” axis.
• Graph 4 showed a line beginning near the intersection of the “x” and “y” axes, steadily increasing upward from left to right, then leveling off parallel to the “x” axis.

As in Step 2, the eighth-graders were to conduct their experiment using an image of a single test tube over which was suspended a metal ball. For this experiment, the test tube was already filled with honey. Students needed to set the temperature beneath the test tube anywhere from 10 to 100 degrees Celsius. They then had to click on the “Drop” button on the screen, causing the metal ball to drop into the test tube. An onscreen table automatically recorded the type of liquid, the temperature setting, and the time it took for the ball to drop to the bottom of its test tube. Students could click on a “Reset” button, change the temperature, and perform the experiment as many times as they wished.

When an adequate range of data was sampled, results showed that the flow rate of honey increased with temperature and then leveled off at approximately 55 degrees Celsius. Twenty-nine percent of eighth-graders could gather accurate data and select the correct graph representing a complex data set (Graph 4). If students did not test an adequate range of data, they may only have noticed that the flow rate of honey increased with temperature, but may not have recognized the plateau that emerged in the data (which was indicated in the correct option, Graph 4). Thirty-eight percent selected the linearly increasing Graph 2 for their answer.

Try It Yourself: Users can perform the experiment and view the data table using the animation presented onscreen.

Step 5 – Students select the best temperature for bottling honey:

The second part of the final task consisted of the following scenario: The food processing company wants to bottle the honey as quickly as possible while using the least amount of energy to heat the honey. (Assume that the honey has already been pasteurized.) Which temperature range is best to use for bottling honey to meet both of these conditions? Students were to select one of these options:

• 25-35 degrees Celsius
• 40-50 degrees Celsius
• 55-65 degrees Celsius
• 70-80 degrees Celsius

As in Step 4, the eighth-graders were to conduct their experiment using an image of a single test tube filled with honey over which was suspended a metal ball. An onscreen table showed previously recorded results at temperatures of 25, 30, and 45 degrees Celsius. Students could use the “Reset” and “Drop” buttons to change the temperature beneath the test tube and perform the experiment as many times as they wished. Their results were automatically added to the onscreen results table.

Once the plateau in the flow rate of honey was reached, heating it further would waste energy, so the best temperature range for bottling honey was option C— 55-65 degrees Celsius. Thirty-eight percent of eighth-graders selected the correct temperature range for bottling honey. Nineteen percent of students were also able to support the correct selection with an accurate explanation.

Try It Yourself: Users can perform the experiment and view the data table using the animation presented onscreen.

SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2009 Science Assessment.