For many historians the existence of the Boiotian shield during the classical age seems rather doubtful, drawing on the opinion that coins found in Boiotia dating from the classical age who do depict Boiotian shields are merely images projecting the heroic past of Boiotia. Some other writes, however, including Peter Connolly, support the idea that the Boiotians actually used the Boiotian shield during this timeframe. But according to this opinion it was not used in a classical hoplite phalanx due to the different grip and shape of the Boiotian shield, which inevitably left parts of the body unprotected and gaps in the line vulnerable to attack. Peter Connolly and others who follow his thesis suggested that this shield was used in a more open formation along with a longer spear like a pike in order to exploit the moon-cuts of the shield. It is said that Boiotian shield was much lighter and cheaper than the Argive hoplon since it was made from leather and covered in wood. That explains why no shield of this type has ever been found, and also makes the historians believe that poor Boiotian citizens used this shield because of the comparatevily low cost.
Later, during the life of Epameinondas, when democracy had been established and many poorer citizens joined the army, the Boiotian shield became common among their ranks. If we may have an opinion on this, we support the idea that the Boiotian shield existed during the classical era and was more than simply a symbol of the heroic past. It was a shield commonly used by poor Boiotian citizens, who were not able to join the ranks of hoplites. But when democracy was established and many of the poor joined the Theban army in a more professional role, Epameinondas, inspired by the great Athenian general Iphikrates, (Iphicrates created an unit of peltast-hoplites carrying much longer spears and the smaller and lighter pelte shields. Look for the Iphicrateans in the Athenian preview) armed those who carried Boiotian shields with pikes and deployed them in a more open formation than the classical hoplitic phalanx (as Connolly says) in order to fully exploit the elements of the shield and make them robust enough for a fight with heavy hoplites.
Another reason to strongly believe Connolly's theory is the example of Philip II of Makedon. It is commonly known that Philip was strongly inspired to reform the Makedonian army from what he saw in Thebes. But what exactly did he see there in order to create an army full of pikes? That's why we believe that Iphikrates started the development when he created his peltast-hoplite soldiers using all the lessons of the Peloponnesian war, Epameinondas was inspired by him and finally Philip used all the knowledge from his time in Thebes to invent a perfect army full of those soldiers with pikes and pelte shields, the Makedonian phalanx. We do not actually know how the afore mentioned troops were used by the Thebans so we can only speculate that they normally filled the last ranks of the Boiotian phalanxes in order to achieve the huge depths of 25-50 ranks. At least this may have been be their initial role before Epameinondas trained them and exploit all their benefits to make them into a force like the later Makedonian phalanx. Unfortunately its creation had to wait until the rule of Phillip in Makedon because of Epameinondas' early death at the battle of Mantineia.