Setting up a control experiment - understanding the key principles

Science students often struggle to understand the concept of a control investigation, something which is regularly examined by most exam board specifications. This worksheet explains clearly what a control investigation is and then provides several practice investigations which require students to describe a suitable control. Finally, the worksheet provides an extra 'challenge' question for more able students to describe how control experiments were important in establishing the germ theory of disease and debunking the myth of spontaneous generation.