Didn't the Sacred Band of Thebes defeat a numberical superior army of Spartans at the Battle of Tegyra. also at Leuctra against the Spartans as well.
True

I'm not very familiar with Tegyra, but Leuctra is usually considered to have been a tactical innovation on the part of the Thebans. The details are disputed (was it an echelon formation or oblique line with refused right flank, for instance?) but the Thebans deployed on the left, rather than the right so they met the Spartans. This prevented the usual Spartan battle plan of routing their enemy's left then wheeling about to "roll up" the rest of the line (being the only hoplite army well-drilled enough to perform any complex manoeuvres in the field). It still seems though that the extra depth of the Theban phalanx was the crucial factor in breaking the Spartans, and once they'd gone down there was no way the rest of the army was going to stay in the field. Overall I still think this was more a victory of inspired generalship than a superior elite.