Here is a resource with a descriptive approach to explaining the scientific method. It's simple, but effective for both introduction and reinforcement of this concept. 

In this bridge design worksheet, pupils answer 5 general questions about bridges. Students follow the directions to construct 4 types of bridges with paper and test them for strength.

In this pollution learning exercise, students read about thermal pollution and how hot water affects wildlife. Then students complete 1 short answer question.

In this paper helicopter worksheet, students design and experiment making a paper helicopter to explore how some things fall and how varying the size of the rotor blades affect the way a helicopter spins.