Whether your young scientists are conducting indoor plant experiments ("What conditions promote the best bean plant growth?") or outdoor habitat research ("Which plants do different types of butterflies prefer?"), they'll need to practice accurately gathering and organizing their data. By learning how to represent their data so patterns are revealed, students will be able to make better sense of their experiences. This article describes some plant-related challenges, and suggests strategies to help your students think and act like scientists as they grapple with data from their indoor and outdoor gardening experiences.
What students choose to observe and measure will depend, in part, on the nature of their question, experimental setup, hypotheses, and so on.
To help students decide what types of information to gather, you might first have to help them clarify the language in their question or hypothesis. For instance, with plant-related investigations, students often want to know which treatment will result in the "best" plant growth. Challenge them to define what they mean by "best" and imagine what type of data would support their predictions or hypotheses: the tallest plant? The greenest? The one with the most leaves? Once they've answered these questions, they can better clarify what they'll observe and measure. (Consider starting by brainstorming a list of the factors that students might look at: height, number of leaves, color of leaves, number of branches, root length and shape, stem width, leaf area, distance between nodes, and so on, then choose some that students believe may be the best indicators of plant health.
A similar challenge with classroom data gathering is the need for "standards" of measurement. This is particularly important if you have a number of students or groups working on different aspects of one investigation. "We had several classes working together on an investigation of light tubes," says fourth grade Chicago, IL, teacher Paul Scott. "When students first started posting data, some noticed that there was no uniformity in the way people were taking plant height measurements. Some were measuring from the soil to the end of the longest branch, while others measured from the lowest branch to the end of the top leaf. Students quickly realized that we needed to establish a standard." You might choose to establish (and practice) measurement standards up front, or let students discover the need themselves (with your questions and guidance) as they conduct and review their investigations.
While some data are obviously quantifiable, such as measurements of height, length, mass, volume, or responses to a survey, other observations may be more qualitative, based on sensory descriptions of objects and phenomena (e.g., how worms respond to light). Older students may be able to create more subjective comparisons by quantifying descriptive information. If students were comparing leaf colors, for instance, they might use magic markers to identify different shades, then assign a score to each of the three or four shades, and compare average scores between plants in the treatment and control groups.
Observation is one of those skills teachers assume students have. But without guidance, student observations often lack detail and precision. Giving students adequate time to observe carefully, providing tools (e.g., hand lenses) to enhance observations, and encouraging detailed descriptions with precise language and drawings can improve students? observations and encourage them to think and act like scientists.
"When my sixth graders set up plant experiments," reports LaCrescent, MN, teacher Scott Tyink, "they often chose to look at only one factor--plant height, for instance--but later they began to notice other factors like the leaf color, shape, or flowers. It can be a challenge to persevere and sift through data. Sometimes students realized in the midst of experiments that they hadn't collected enough data or collected it well enough to make sense of it. This helped them understand the need to plan and sometimes revise investigations."
By structuring how students record their observations, you can help them recognize the importance of organizing the information they gather. GrowLab forms that help students record their investigation observations and data include "My Plant Journal" for younger students and the "Observation Journal" for older students. Both are located in GrowLab: Activities for Growing Minds. A science journal or notebook is another tool for documenting investigations. One technique for structuring entries is to have students divide each journal page, with one half for observations, drawings, and measurement, and the other half for thoughts and questions prompted by their observations.
To get students in the habit of systematically recording experimental data as scientists do, consider using data tables. A data table is typically a titled chart that includes the manipulated or independent variable (e.g., soil type) in the lefthand column and the responding or dependent variable (e.g., time it takes to drain a cup of water) in the next column. If students repeat the trial for each variable or collect data from a number of groups, they can include a third column to record an average (e.g., average drainage time. The information from a data table can later be transferred to a graph so patterns are more easily revealed.
To be able to make sense of information gathered during a plant investigation -- compare results, find patterns, and make explanations -- it helps to have a visual overview of the information. There are many ways to organize data from an investigation including "before and after" drawings, concept maps, classification schemes, oral descriptions, and models. Older students can create more sophisticated organizers and review data taken over time and/or from multiple experiments. Here we will focus on different types of charts or graphs.
Have students consider what information they are trying to depict. By exposing students to different types of charts or graphs, helping them understand when it's most appropriate to use each one, and modeling how to create each type, you will prepare them for making appropriate choices as classroom scientists.
HISTOGRAM - Students should use this type of bar graph when they want to represent frequencies -- for instance, the number of students surveyed who have x as a favorite vegetable.
PIE CHARTS - These are used to depict parts of a whole -- the fraction of the garden that is devoted to herbs, vegetables, annuals, and perennials, for example.
BAR GRAPHS - These should be used to show comparisons of data with discreet categories such as days to germination for different types of vegetable seeds.
LINE GRAPHS - Upper elementary students might use these to show correlations among variables when the intervals on each axis are equal and continuous (e.g., height, time, temperature, volume). For instance, students could use a line graph to depict how incremental amounts of fertilizer affect plant height. They would choose a bar graph to depict how different soil types affect the size of leaves plants produce.
Because plants (ideally) grow continuously, many of your students' experiments will involve tracking change in plant growth over time. In these cases, students might construct a line graph with the dependent variable (e.g., height) on the y axis, time on the x axis, and plot a set of points for each independent variable (for example plants grown in soil, sand, and clay).
All charts should be titled, and graphs should include the manipulated variable (independent) on the x the responding variable (dependent) on the y axis, and feature labels and units for each. Students should be able to plot points from their data tables on line graphs, then draw a "line of best fit" between or near data points that offers a visual image of the correlation between variables. Students should be able to write a sentence or two that summarizes the data (e.g., As the amount of fertilizer increased, the intensity of green leaf color increased).
Teachers often find that student-designed graphs make poor use of space. One method for helping students choose appropriate intervals for measurements on an axis is to have them first find the difference between the smallest and largest values for a variable, such as height. (They can use these values for the bottom and top of the axis.) If they divide the difference by five (an arbitrary number that seems to work well) and round to the nearest whole number, they'll get a number that they can use for the intervals on that axis.
"With a goal of honing my fourth graders' metric skills and encouraging them to think about fair tests, I set up a contest to see which small group could grow the 'biggest' lima bean plant, "reports Nashville, TN, teacher Nancy Johnson. To decide how to determine the "biggest" plant, students first used rulers to measure heights of standard objects to improve measurement skills, then measured the heights of their group's plants. "Students wanted to measure the heights of the other groups' plants too," says Nancy, "to be sure that the 'competition' was also measuring correctly!" To reduce individual competition and increase cooperation, students decided to total the sizes of each group member's largest plant. Each child made an individual data table for his or her journal, and the class made a group data table to track the whole contest.