Students find it challenging to think scientifically when it comes to understanding and designing experiments. “This skill . . . . commonly known as ‘control of variables ability’” (Tairab 2016) is the ability to carry out controlled experimentation in which, ideally, only one variable is changed by the student researcher, while other variables are held constant. Various studies cited by Tairab found that students have difficulty with these concepts from both procedural (manipulation of variables) and logical (evaluating relationships) standpoints.

The activities described here challenge students to design and build two iterations of a simple tower, the second involving control of variables. Then, through class discussion, we use the activity to review the concept of variables and clarify how variables may be manipulated and evaluated. The activity and subsequent class discussion lead us to elaborate on the testing of an independent variable while controlling as many other variables as possible.

I introduce this activity as a formative assessment on the second or third day of school, giving all of us (students and myself) an opportunity to assess whether the students have a foundation in recognizing a controlled investigation and identifying variables. This lesson is fun, collaborative, and a good way of kicking off the academic year while reviewing basic concepts. It serves an additional function of which the students are unaware; it gives me an opportunity to observe their ability to collaborate and cooperate with their peers, information that I will draw on when establishing working groups in the future.

Entrance slip

On entering the classroom, provide each student with a quarter sheet of blank paper and ask them to write their name and, as best they can, to describe what a variable is; alternatively, students can use a digital entrance slip with the same objective. At this early point in the academic year, students may or may not be able to articulate an adequate explanation. Assure the students that they will not be graded on this; it is a simple preassessment. Then ask the students to set this slip aside until it is revisited at the end of the activities.

Activity 1

I place students in groups of three to four according to where they are sitting because I do not know the students well enough this early in the academic year to group them on the basis of skill level. Provide each student group with a container of presorted supplies and a meter of masking tape. The supplies can be any objects that students can tape together (e.g., straws, toothpicks, bottle caps, Lincoln Logs, paintbrushes, race cars, paper cups, paper bowls, pasta). Each set of supplies for this activity consists of the same number of items, but different items. For example, one group might receive two long Lincoln Logs, three straws, a bottle cap, and a toothpick (seven total items), whereas another group might receive four bottle caps, one short Lincoln Log, one straw, and one toothpick (also seven items). See sample tower in Figure 1 on first page of article. Although this activity is basically safe, students should wear goggles to avoid injuries in their enthusiasm to build quickly. Moreover, students should have completed a classroom safety contract prior to engaging in hands-on activities.

Student groups are instructed to build the tallest tower they can in five minutes; they are also told that they may not trade items with another group. One thing I often hear at the beginning of this activity is, “We already did this in [a previous] grade.” I simply comment that this activity is a little different. Pretty quickly they understand why, and that concern promptly settles itself.

Students are quick to take on the competitive nature of the activity. They will, however, quickly look around and realize that each group’s supplies are different and realize that their outcomes will consequently differ as well. It is important to not let this stage go on very long because occasionally a student may become frustrated with the “unfair” nature of the supplies (this has happened to me on only a couple of occasions over several years). At the end of five minutes, take note of the range of shortest to tallest tower. It is unnecessary to document the height of each group’s tower, but it is helpful to use the range as a discussion starter. The group with the tallest tower is always pleased, and a compliment to each group about their ingenuity smooths any ruffled feathers.

Discussion 1

Begin a class discussion in which student thoughts are elicited. I find that the vast majority of students are too embarrassed to be confrontational, but there is at least one in every crowd who will accuse me of being unfair or of rigging the outcome. Once that door is open, our discussion turns to how/why the competition was unfair. This is when I steer the conversation to “What are variables?”, seeking to encourage students to “determine relationships between independent and dependent variables in models” (NGSS Lead States 2013). In a 10-minute discussion, we are able to re-establish the concept that “variables are different factors that could affect the outcome” (Llewellyn 2007, p. 121) of an investigation. Since a “manipulated variable or independent variable is the variable that affects the outcome” (Llewellyn 2007, p. 121; italics in original), in this activity, the obvious independent variable is the building materials supplied. Moreover, because a “responding variable or dependent variable” change[s] as a result of the manipulated variable” (Llewellyn 2007, p. 121; italics in original), the height of the towers in this activity is the dependent variable. With so much variation in the supplies, this is not a fair competition nor a valid “experiment” because there is not a single independent variable with a set of controlled variables, other than time and the one-meter of tape.

Our discussion of “fair or not” is not yet finished, however. When I ask the students what would make the contest fair, they immediately determine that it would be fair if they all had the same supplies. I record their suggestions for how to accomplish parity, and as a class, they settle on which objects each group should have. I promptly redistribute supplies such that each group has not only the same number of items, but the same items as well. (Plan ahead for this stage; be sure that there are at least one per group of every item—six long Lincoln Logs, one per each of six groups, etc.).

Activity 2

As soon as the supplies are equitably distributed, the students again have five minutes to build the tallest tower. Measure the towers again before the wrap-up discussion and note the range in tower heights. Typically, the group with the tallest tower wants to know what the prize is; I usually just say, “bragging rights.” I don’t offer a reward because some of the students were a little annoyed by the end of Activity 1, and I want them to let that go. Also, I want to set a tone that it is better in my class to try new things and learn collaboratively rather than compete for individual superiority. The diversity of tower height and design does, however, provide an excellent context for our follow-up discussion.

Discussion 2

A well-constructed scientific investigation changes only one variable at a time whenever possible, whether that investigation is an experiment, a design challenge, or an opportunity to collect observational data. The variables that one can identify may include those that the experimenter has chosen to change (the diverse building materials in Activity 1), those that are kept the same (such as the building materials in Activity 2, as well as time and tape), the outcome of the investigation (such as the tower height measured here), and perhaps the context in which the investigation takes place. This second discussion begins by prompting students to again identify these factors. This discussion achieves the learning objective for the class; it is the point at which the concept of variables is confirmed.

In Activity 2, just as in Activity 1, the tower height is the dependent variable. Measuring the towers will show that despite controlling the building materials and time, the towers are inevitably different in height and design. This is an opportunity for the students to extend their thinking beyond the items at hand. A little prodding may be required, but at least one student will recognize that their own ingenuity determined their tower design. Because a variable is any factor that can affect the outcome of an activity, their independent variable is their own creativity and collaboration. One of the wonders of science is that it is an inherently creative enterprise, and the added value to this activity is that the towers are a visible display of originality.

Exit slip

Before leaving the classroom, have the students use the other side of their entrance slip to revise their thought(s) about variables. Ask them to try to explain controlled, independent, and dependent variables. Also, ask them to label this as side two of the paper to make clear the evolution (or not) in their thinking. Collect these; they can serve as a formative assessment and as documentation of student conceptions. Later, they provide the foundation for formal lessons on the nature of science (see Online Resources) because I am able to use the students’ own conceptions and misconceptions to guide my planning for future lessons. Specifically, I am able to identify which students are grasping the main ideas and who needs more assistance, and thus I can design future lessons accordingly.

During a subsequent class I have students record and define the types of variables in their science notebooks and support each definition with examples from this activity. As the year progresses, they become adept at designing their own investigations. For example, later in the month, when students were asked how we might explore biodiversity on campus, they were able to measure the same-sized space (control variable: 1 meter circle) in different areas (independent variable: pond, woods, field) to identify the variation in number of plants found (dependent variable). Afterward and throughout the quarter, when students struggle with the concept of variables, I am able to invoke the variables the students identified and manipulated in these simple activities to refresh their conceptions.

Variations/Extensions

Due to COVID-19, I modified the activity last year to use disposable items instead of materials that must be disassembled and saved for the next class. In this manner, students were socially distanced and avoided touching and sharing items. For example, each student received a paper plate with a set of pieces of pasta as well as their 1 meter of tape; I washed my hands while collecting supplies, before passing out supplies, and after passing out supplies. These were prepared in advance for Activity 1 with mismatched sets of pasta; a second stack for Activity 2 contained matched sets of pasta. Despite having separate plates of supplies, the students showed me their collaborative natures through their camaraderie and shared building ideas (see Figure 2).

This activity is designed to be a simple starting point for the year and a getting-to-know-you activity. I use it on the second or third day of school to collect students’ brief written summaries as well as mostly observational data about my new students’ collaborative skills, confidence, and conceptions of the nature of science. No summative assessment is associated with the activity as I have described it here. Another teacher may wish to evaluate student performance more formally. For example, students may be asked to write a summary of the activity in which they demonstrate their knowledge of these types of variables. Alternatively, they could be asked to use their understanding of variables to design a simple experiment. •

Online Resources

NSTA Position Statement on the Nature of Science—https://www.nsta.org/nstas-official-positions/nature-science

Anne Farley Schoeffler (schoefflera@setoncatholicschool.org) is a middle school science teacher at Seton Catholic School, Hudson, Ohio.