Have you heard of pattern games for dog training?
If you're in the positive reinforcement training community, you likely have!
They are very simple and have been used unknowingly by many trainers, but the one trainer who brought large scale attention to them recently is Leslie McDevitt, creator of the Control Unleashed program.
She built an entire program for sport dogs based around pattern games to calm arousal and more.
As the methods grew in popularity, she learned that the pattern games were hugely effective for reactive dogs as well - not just overexcited sport dogs.
Reactivity is a response to distractions usually characterized by barking, lunging on leash, pulling on leash, jumping, whining, growling, and more, especially in response to other dogs or people.
A very common example of reactivity is a dog who barks at visitors to the door or outside the window.
Reactivity can have many root causes including excitement or anxiety.