you are a mean professor... but "es" would be "eres" instead.
Ella es una chica mala
La profesora es... *and you insert her name here*
You are a bad teacher/professor. (female) Unless you are being intentionally disrespectful, you normally wouls not address a teacher or professor in the tu form.
Is your mathmetics professor a man or a woman.
who is the professor
You need the la before professora. It would then translate over to: "She is the teacher"
"ella es una chica" means "she is a girl" in Spanish.
"¿De dónde es la profesora?" in Spanish means "Where is the teacher from?"
es una clase de matematicas means is a kind of mathematics
It means "it is one" referring to a feminine noun, e.g. es una mujer = it's a woman.
"Una palabra nueva es" translates to "a new word is" in English.
"La maestra es una pendeja" translates to "The teacher is an idiot" in English.