Article excerpt

A hypothesis is a rather sophisticated concept for middle school students to understand. The standard definition, an educated guess, while serviceable, unfortunately undermines the important idea that a hypothesis is more than a guess, which implies something random and not clearly grounded in explanation. A hypothesis is better described as a tentative explanation. Elevating the hypothesis to an explanation that can be tested underscores the nature of scientific inquiry. Developing a hypothesis is one of the critical tasks of the Next Generation Science Standards science practices (NGSS Lead States 2013). Developing a testable hypothesis is one of the essential steps of proposing an explanation for the relationship among variables (see Figure 1).

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One method of helping students create their own hypothesis is to ask them to frame it as an "If... then..." statement, which emphasizes the relationship between two variables. Examples might include the following:

* "If I shine a lamp on the watered bean seed, then it will grow more than a bean seed that does not have a lamp shining light on it."

* "If I add a piece of candy to a bottle of diet soda, then it will cause the soda to foam up and shoot out of the bottle."

* "If I add salt to a cup of water, then it will take the water longer to come to a boil."

The value of this approach is that it focuses on the relationship between a hypothesized cause and effect--the student is engaged in seeking relationships. The next intellectual step is to explore an explanation for the relationship. In the same way that the "If... then... " statement helps students formulate their first efforts at composing hypotheses, an "If... then... because... " construction helps students understand that at its heart a hypothesis searches to better understand why a relationship exists.

Examples of hypotheses constructed using "If... then... because... " include the following:

* "If I take a recently sprouted seedling and point it 'upside down,' then it will change direction and grow upward because of the influence of geotaxis on plant growth."

* "If I shorten the length of a pendulum, then the period of the pendulum will decrease because the period of a pendulum is a function of the length of a pendulum."

* "If a plant is fertilized, then it will grow to be taller than a plant that does not receive fertilizer because of the additional nutrients present in the fertilizer."

What is present in these examples is a statement about the nature of a relationship. If a hypothesis is defined as an educated guess, the "because" portion of each statement establishes the "educated" part of the hypothesis as a meaningful explanation that relates the cause and the anticipated effect. The test of the hypothesis that the student will carry out becomes more about examining a proposed explanation between a cause and an effect than simply confirming that a proposed cause and effect exists. As documented in the Next Generation Science Standards, by grades 3-5, students should learn how to ask questions about what would happen if a variable is changed. By grades 6-8, students are required to ask questions to determine relationships between independent and dependent variables and relationships in models (NGSS Lead States 2013).

The guided-discovery activity that follows is designed to help students develop a better understanding of the idea that developing a hypothesis involves testing an explanation. The activity is grounded in the content associated with understanding physical changes associated with matter. The learning objectives for students are as follows:

* Develop and test a hypothesis describing changes in mass of coins over time.

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* Interpret and analyze the data gathered during the experiment and provide an evidence-backed explanation of the changes observed. …

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