Design a cheap 1.5V / 12V DC motor driver for high school students
One simple way would be to use a DPDT switch using the following arrangement. You could also include a pushbutton after the battery if required for momentary operation and there are also switches available that have a center position that is off. Just make sure to use a break-before-make switch so that you don't get any shorts:







simulate this circuit &ndash; Schematic created using CircuitLab