Yes you do need an incubator.  Bacteria aren&#x27;t a simple chemical reaction that just runs more slowly at room temperature.  Many bacteria that live in your mouth will not grow at all at room temperature.<p>I&#x27;m not saying someone couldn&#x27;t hack together this experiment.  I&#x27;m saying a middle-schooler who can walk into a lab and prepare everything in an afternoon under professional supervision is at an advantage compared to a middle-schooler who has to gather all this equipment and knowledge over the course of weeks and months (which will still be inferior from a non-didactic point of view) without the support of their parents when it comes to performing a valid scientific experiment.