NSES Content Standard A 
Science as Inquiry: Understanding about scientific inquiry
Grades 5-8, page 148

Current scientific knowledge and understanding guide scientific investigations. Different scientific domains employ different methods, core theories, and standards to advance scientific knowledge and understanding.

Benchmark 1A The Nature of Science: The Scientific World View
Grades 6-8, page 7
Scientific knowledge is subject to modification as new information challenges prevailing theories and as a new theory leads to looking at old observations in a new way.

Benchmark 1B The Nature of Science: Scientific Inquiry
Grades 3-5, page 11
Scientists' explanations about what happens in the world come partly from what they observe, partly from what they think. Sometimes scientists have different explanations for the same set of observations. That usually leads to their making more observations to resolve the differences.

Benchmark 1B The Nature of Science: Scientific Inquiry
Grades 6-8, page 12
Scientists differ greatly in what phenomena they study and how they go about their work. Although there is no fixed set of steps that all scientists follow, scientific investigations usually involve the collection of relevant evidence, the use of logical reasoning, and the application of imagination in devising hypotheses and explanations to make sense of the collected evidence.