The most useful technique to help solve the problem of Evan hitting children when he doesn't get his way is positive reinforcement. Positive reinforcement involves rewarding desired behavior to increase the likelihood that it will be repeated.
In this case, Evan can be rewarded for playing nicely with other children and using his words to express his feelings instead of hitting. This can be done by praising him when he behaves well, giving him a small treat or toy, or allowing him to participate in preferred activities.
Through positive reinforcement, Evan can learn that playing nicely and using his words is a more effective way to get what he wants than hitting. This can help to reduce his hitting behavior and improve his social interactions with other children.