"What surface has the most bacteria?"
This science activity is perfect for practicing the scientific method.
Rub potato slices all over different surfaces (doorknobs, shoes, desks, etc.) and observe the mold that grows on them over the course of a week or two.
Pages are include for students to write a hypothesis, identify the variables, and record their observations (chart). A list of materials and a step-by-step procedure is included, but there are also lined pages available if you would like your students to write their own.