Hi Kevin :-) I thought of two possible causes for your flat cookie problem. First make sure that your baking powder isn't past it's pull date. Secondly, get an oven thermometer and check to make sure that your oven is at the temperature you think you are setting it at. If it is not as hot as it should be, your cookies would spread and be thinner than they should be. I hope this has given you some things that you can check and maybe, find the cause of your problem. Good luck!