They work via the "Ideomotor effect"--Slight subconscious movements of the motor muscles of the hands and arms. Other such ideomotor devices include the Chevreul pendulum, used by Psychologists to probe the subconscious mind, dowsing rods and table tipping.
The Board is a TOOL to communicate with the SUBCONSCIOUS MIND at least.--That is accepted by most psychologists.
Spirit communication may be possible too, many folks think, as our "Latent ESP" is also said to live in the Subconscious mind.----In theory, A spirit uses the subconscious ESP of the board user to communicate, telepathically or clarivoyantly.
This is why more than one person operates the board, to keep the subconscious mind of any one person from taking over the board, Only the common ESP message from the spirit will thus come through.
I would not buy it for a Kid. It takes a bit of "maturity" to operate the board and not jump to crazy conclusions or take the messages too seriously.
So the board communicates with the SUBCONSCIOUS mind, that aspect is not contested, it DOES work. Those who believe in ESP also say that this subconscious mind can also contact what we call "spirits"---Perhaps it can.
Scientist with years of paranormal study on the side