Yup, and from the early chapter and the anime, we clearly see that Yukari and Moka is really smart being #1 and top ten in an exam. Kurumu and Mizore is not good unfortunately (from math exam in Ririko-sensei arc, we see Kurumu is the worse
getting 44 while Yukari get 100 and Tsukune get 80+), Tsukune is too distracted about the chaos in the school (but actually he can if he is study).
Don't know about Ruby yet... I bet she is pretty smart because she is a witch that usually smart from the beginning.