Findings from the TIMSS 2019 Problem Solving and Inquiry Tasks

Ina V.S. Mullis, Michael O. Martin, Bethany Fishbein, Pierre Foy, and Sebastian Moncaleano

Chapter 4: Science Grade 8

Pepper Plants

Screen 3 – Experimental Setup: Soil and Plants

This screen introduces the experimental setup for testing the fertilizers, which consisted of three growth tanks each containing the same amount and type of soil and 24 seedlings. Students were asked to explain why having 24 seedlings in each tank constitutes a good setup for an experiment. Students obtained credit (1 point) either by explaining that having the same number of plants in each tank constitutes a fair test or that having a large number of plants in each tank accounts for plant-to-plant variations (reliability).

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Maximum Score Points: 1
Content Domain: Biology
Topic Area: Ecosystems
Cognitive Domain: Reasoning
Science Practice: Generating Evidence


Exhibit 42 shows that on average across countries, 27 percent of students answered the item correctly. Explanations based on the nature of a fair test were more common (18%) than explanations based on the reliability of the setup (8%). That almost three-fourths of the eighth grade students did not provide a correct answer was worrisome, but as the task progressed somewhat greater percentages of students displayed understanding of the nature of a fair test. On average, a higher percentage of girls than boys answered this item correctly (29% vs. 24%).