OH, do I know what you’re talking about here! It’s hard for any good parent, but even harder to walk that line when it’s in an area you love.
My best advice is to ask more questions than you make declarative statements, even if those questions are highly leading ones.
Don’t tell her, “Well, you’ll need a second plant for your control.” Ask her, “If you give this plant fertilizer, how to you know it’s made any difference in its growth?”
Don’t tell her, “Remember to change only one variable,” instead ask, “Hmmm…how do you know if it’s the brand or the *age *of the orange juice that affects how much Vitamin C is in the OJ? Could a different storage material make an impact? I see juices are available in paper boxes, in clear glass and in plastic… Can light get through all of these the same?”
Instead of, “This website says we can bake soil to kill all the microorganisms in it and see how that affects plant growth,” try, “What things kill microorganisms?” (Heat, soap, etc.) “What do we have that makes a lot of heat that won’t damage dirt?” (oven) “How hot and how long does something have to be heated to kill microorganisms on it?” (google is your friend!) “What’s that called, anyway?” (sterilization) Bonus nerd points if she thinks of the pressure cooker and invents autoclaving on her own!
When it comes time to present the data, teach her how to set up a table, graph or chart of the type she’ll need, but do it with different data on a different topic, and then see if she can apply that knowledge to her own data set. So show her how to chart using, say, the number of pets she and her friends own, or what percentage of her stuffed animals are bears. Then see if she can figure out how to make a chart for her actual project. That way you don’t run the risk of charting her data for her, and she learns how to chart.
The visual presentation can be done very well by her with the aid of a computer and word processor, although she might need some help with layout ideas. Making a small scale sketch and outlining some boxes in light pencil on her poster board can help her get an idea of how big to make words and pictures and graphs to best use the space she has. Lots of unaided projects end up with 12 words squished in the upper left hand corner and vast deserts of white space in the lower right.
If you google third grade science fair experiments, you’ll get literally more than a quarter million hits. Lots and lots of ideas out there! Good luck, and have fun!