Teaching calm-down strategies and using anxiety and anger management worksheets are proven cognitive-behavioral techniques used by professionals. Like any change in habit, you can't expect instant results, but rest assured, over time, you can expect lessened outbursts, more awareness, more thoughtfulness, and kindness (to name a few). You can't expect to eliminate tantrums or other unwanted behavior completely. The idea is not to stop anger or anxiety completely, that's not possible, the goal is to help kids learn how to react more appropriately. Most importantly, have fun with this!
If you or your child is in crisis, you need to seek the help of professionals, these resources are not meant to replace the advice and guidance of your doctor or health care professionals.