There are stories of women teaching from behind a mechitza (I believe Nechama Leibowitz did so?).
But here's one Gemara, Pesachim 62b:
ר' שמלאי אתא לקמיה דרבי יוחנן. א"ל: ניתני לי מר ספר יוחסין
...
ניתנייה בג' ירחי!
שקל קלא פתק ביה א"ל: ומה ברוריה דביתהו דר"מ ברתיה דר"ח בן תרדיון דתניא תלת מאה שמעתתא ביומא מג' מאה רבוותא ואפ"ה לא יצתה ידי חובתה בתלת שנין-- ואת אמרת בתלתא ירחי ?!
Rabbi Samlai approached Rabbi Yochanan ... and requested that Rabbi Yochanan teach him The Book of Lineages in three months. Rabbi Yochanan replied: Bruriah, the wife of Rabbi Meir and daughter of Rabbi Chananya ben Teradion, could teach 300 topics a day from 300 insights -- and even she couldn't do the entirety in three years! You expect me to teach it to you in three months?!
Rashi says this Book of Lineages is: מתני' דדברי הימים. Our Oral teaching on Chronicles.
So the Gemara pretty much says that Bruriah taught this Talmud-like work (which is no longer extant). Make of that what you will.
Though see Alex's question and my response below -- some translate this as "she learned" rather than "she taught."