It can be a challenge to come up with a high school science fair project idea. There is fierce competition to come up with the coolest idea, plus you need a topic that is considered appropriate for your educational level.  The hardest in that almost everyone has to do one, plus it's usually for a grade are high school science fair projects. You want a topic that causes the judges to take notice. Look at topics addressed by others and ask yourself what questions are left unanswered? How could they be tested? Look for problems in the world around you and try to explain them or solve them. Demonstrations and models might be acceptable at earlier educational levels, but in high school the scientific method should be the basis for your scientific exploration. How much is the interior of a car cooled if a light-blocking windshield cover is used? Do they work? How sterile is contact lens solution and how long does it stay sterile? See how long it takes for mold, fungi, and bacteria to culture saline. How sterile is the inside of a person's contact lens case for that matter?

High school science fair projects

Can you make your own musical instrument that can play a complete scale? Examples might include a rubber band harp or flute from clay, wood or plastic. How do different fertilizers affect the way plants grow? There are lots of different types of fertilizers, containing varying amounts of nitrogen, phosphorus, and potassium, in addition to other ingredients. You can test different fertilizers and see how they affect the height of a plant, the number or size of its leaves, the number of flowers, time until blooming, branching of stems, root development, or other factors. Does using colored mulch have an effect on a plant? You can look at its height, fruitfulness, number of flowers, overall plant size, rate of growth, or other factors. How do different factors affect seed germination? Factors that you could test include the intensity, duration, or type of light, the temperature, the amount of water, the presence/absence of certain chemicals, or the presence/absence of soil. You can look at the percentage of seeds that germinate or the rate at which seeds germinate. How are plants affected by the distance between them? Look into the concept of allelopathy. Plans that elease chemicals (allelochemicals) that can inhibit the growth of plants near them are sweet potatoes.  How close can another plant grow to a sweet potato? What effects does an allelochemical have on a plant? Is a seed affected by its size? Do different size seeds have different germination rates or percentages? Does seed size affect the growth rate or final size of a plant? How does cold storage affect the germination of seeds? Factors you can control include the type of seeds, length of storage, temperature of storage, and other variables. What conditions affect the ripening of fruit? Look at ethylene and enclosing a fruit in a sealed bag, temperature, light, or nearness to other pieces or fruit.