We know our class read 475 hours. Whenever anyone notices a pattern, or speculates about a pattern, ask them to provide evidence that the conjecture holds by finding enough instances that work so that they and others are convinced. Or they can disprove the conjecture by finding an instance that doesn't work. Ask other children to convince themselves of these conjectures, or disprove them. For example, a child notices that two even numbers add up to even numbers, and speculates that two odds also add up to an even.
Mathematical proof means showing a conjecture holds for all possible cases.
Showing thousands of examples that two odds add up to an even may be convincing, but it's not a proof. A proof would explain why two odds must add up to an even for any two odd numbers. Disproving a conjecture is usually an easier process. Finding just one counterexample is enough to disprove a conjecture, because this shows that it does not work for all cases. Whenever possible, try to get students involved in proving conjectures, not just providing evidence.