I have a few kids who have trouble with negation concepts (not, none, nothing, except, etc.). This is a hard concept to teach! I usually start by putting 3 similar noun picture cards in front of the child and saying, "These are all foods." I then put a non-food picture card in front of the child (but away from the others) and say, "But this one is NOT a food." Then I gradually fade the verbal cues until the child is the one saying "This one is NOT a ______." I made this worksheet to make the concept a little more abstract (i.e., without using picture cues).