A turn board is a slim rectangular board which works on the principle of reducing friction between the foot and the floor, allowing the dancer to spin fast.
It is clear the benefits of turn boards can be debated, and it seems dance teachers are divided in their opinions of turn boards. It is unclear as to whether turn boards' aids can be translated directly into improving a dancers' technique. There are many aids, products and remedies for dancers on the market which help their training, but it seems turn boards do not fall completely into this category.
First seen in the dance film documentary First Position, turn boards help dancers to master multiple turns. Some argue turn boards increase dancers' confidence in performing lots of turns, which is correct, however the technique employed to do so without a turn board is very different. Turn boards are used with a flat foot, rather than the relevé of turns and pirouettes, so the dancers' balance is not used the same as how they will turn usually. It can be argued that turn boards encourage incorrect technique, and using one will not mean the dancer can suddenly perform ten pirouettes off the board. Turning on a flat foot means the foot is not in the same position and the weight distribution is different than for pirouettes.
https://www.youtube.com/watch?v=-p3aAq8EpuQ
Therefore, the physicality of a turn, with an adjusted centre of gravity when on flat, demi or full point, is very different with and without the board. For beginners who are just learning turning technique it is likely that the turn board would complicate matters. It could make learning pirouettes harder or encourage bad habits.