A claim about numbers is made, and the question is whether it holds every time, some of the time, or none of the time. These free printable worksheets give the statement and leave room for the example that settles it.
If they get stuck
The answer key prints on a separate page.
"Taking away makes a number smaller" feels obviously true and is only sometimes true, because taking away zero changes nothing. Finding that one case is the work, and it is the beginning of mathematical proof: a single counterexample is enough to demote "always" to "sometimes", while no number of examples is ever enough to promote "sometimes" to "always".
The asymmetry is worth naming out loud, because it is what separates this from a guessing exercise. To argue for "always" a child has to give a reason; to argue against it they need one example. Both are written on the page, and the reason is the part to read.
One question from a sheet like this one, worked a step at a time — with a sentence saying what just happened and why.
Always, sometimes, never, step by step