A student’s science fair project involves studying the effects of fertilizer on grass height. After four weeks of measuring height weekly, the student was not able to tell any difference between two pots of grass he had fertilized and watered weekly. How could this experiment be improved?

In order to investigate the effects of fertilizer on grass height, the student needs to have a control sample. He should only fertilize one pot so he can compare the differences in growth between the two. Measuring more frequently and accurately would still not allow him to make any conclusions since there is no control sample. The student is investigating the effect of fertilizer, not water, so both plants must be given equal amounts of water.