Distinguish observations from inferences and hypotheses from theories and laws, and describe science as an ongoing process of testing ideas against evidence.
Science is a specific method for building reliable knowledge about the natural world: propose an explanation, test it against evidence, and revise it when the evidence demands it. A claim only counts as scientific if it is testable -- if there is some possible observation that could, in principle, prove it wrong. That single requirement, falsifiability, is what separates a scientific question ("does this fertilizer increase plant growth?") from a question science cannot answer ("which flower is prettier?").
Two words get confused constantly. An observation is something detected directly with the senses or an instrument -- a measurement, a color change, a count. An inference is the interpretation layered on top of an observation to explain it. A hypothesis is a specific, testable explanation or prediction, usually written as an if-then statement with a reason attached. A theory is not a guess -- it is a broad explanation that has been tested repeatedly, from many directions, and successfully unifies and predicts a large body of observations, the way cell theory or the theory of plate tectonics does. A law describes a consistent pattern, often as an equation, without explaining why it happens. Theories do not "graduate" into laws; they answer a different question.
Mastery looks like: They can sort statements into observation vs. inference, compare hypothesis/theory/law accurately, and write a hypothesis in if-then-because form.
Common stumbles: Treating "theory" as a synonym for guess, and writing a hypothesis as a question or an untestable opinion instead of a testable if-then statement.