「またね。」[mah-tah-neh] means "[see you] again, (wouldn't you agree?)" but is quite casual. If you are talking with your professor, it's better to opt for 「失礼します」（しつれいします） [shi-tsu-ray-shee-mas] "Excuse me." literally it likens more to "I commit a rude act (by parting)." For friends it's good to stick with 「じゃあ、また」 [jaa-mata] and 「また、ね」[ma-tah-neh], while for elders and professors you can say 「失礼します」 as mentioned earlier, or something such as 「では、また次回」（でわ・また・じかい）"dewa, mata, ji-kai" Until we meet again/ Until next time.