A child should be encouraged to choose a science topic he enjoys studying. The topics may pertain to life science, earth science or physical science. According to Education.com, popular third-grade science-fair project ideas include: how to stop soda from exploding, how to tell minerals apart, how to find latitude and learn about a geographic location and how a compass works.
Students should propose a scientific question or hypothesis related to the topic. A hypothesis is a statement that must be proved or disproved with the data that was collected. Some students may observe an object, take and record measurements and report on their findings. If a child wants to answer the question, "Does fertilizer make plants grow faster?" and believes the answer is "yes," the hypothesis would be, "Fertilizer makes plants grow faster."
Background research should be conducted throughout the development of the science fair project. Research is necessary to help support the findings or correct problems with the experiment's design. Students must correctly interpret the data they have collected and keep careful records of the observations or data.
Some teachers may require a third-grade student to write a short project report. The accepted rule for the length of a third-grade paper is at least three paragraphs. The report should include how the student created the project, what he or she learned from the experience, and a list of sources.
Third-grade students are expected to create a display that showcases their work. The display is usually a three-paneled poster board that consists of photographs, drawings, charts or diagrams. The left side of the panel shows the purpose and methods the student employed, and the right side of the panel displays the conclusion. Most science fair judges prefer a display that shows the intent and results of the experiment. For example, if a child wanted to demonstrate a well-balanced diet, a pyramid chart would be a good method to display the healthiest foods for the body.
Third-grade students should practice describing their project, so they will be ready for visitors at the science fair. Some presentations have time limits. The presentation must describe the experiment and state what was done to support the findings.