"A woman who studies Torah is rewarded, but not as much as a man is, for the reason that she has not been commanded to learn. Anyone who does something voluntarily is not rewarded as much as someone who is obligated to do it is. Even though she is rewarded for learning, the Sages commanded that one should not teach Torah to one's daughter, for the reason that most women don't have the mentality for learning, and they think of Torah matters as being nonsensical. The Sages said that teaching one's daughter Torah is like teaching her trivialities. This is talking only about the Oral Torah, but one nevertheless shouldn't teach her the Written Torah either, but if one did it is not like teaching her trivialities."
- The Rambam, Hilchot Yiseodei Hatorah