Gemara

35b (Mishnah): (If a vow forbids Shimon to benefit from Reuven,) Reuven may teach to Shimon Medrash, Halachos and Agadata, but not Mikra (written Torah);

He may teach Mikra to Shimon's children.

36b - Question: Surely, he may not teach Mikra to Shimon because this benefits Shimon. The same applies to Medrash!

Answer (Shmuel): The Mishnah discusses a place where people take money for teaching Mikra, but not for Medrash.

Question: If the Mishnah discusses a particular case, why didn't it specify?

Answer: This teaches that even where wages are paid both for Mikra and Medrash, one may take only for teaching Mikra, not for Medrash.

Question: Surely one may not take for Medrash because it says "Limadti Eschem Chukim u'Mishpatim ka'Asher Tzivani Hash-m Elokai" - just like I (Moshe) taught to you (Yisrael) for free, you must teach for free;

This should obligate to teach also Mikra for free!

Answer #1 (Rav): One may receive wages for guarding the Talmidim. (Normally children learn Mikra from age five to 10 (Avos 5:21). They do not learn Medrash until they are older, when they need not be guarded.)

Answer #2 (R. Yochanan): One may receive wages for teaching the cantillation.

(Mishnah): Reuven may not teach Mikra to Shimon.

Question: We understand this according to R. Yochanan. According to Rav, does one pay for watching an adult?!

Answer: The case is, Shimon is a minor.

Objection (Seifa): He may teach Shimon's children Mikra.

If Shimon is a minor, he cannot have children!

Answer: The Mishnah is abbreviated. It should say, Reuven may not teach Mikra to Shimon. This is if Shimon is a minor. If Shimon is an adult, Reuven may teach to him and his children.

37b - Question: Why didn't R. Yochanan answer like Rav?

Answer: The Mishnah forbids teaching to anyone Mudar Hana'ah (implying that one may be paid to teach to anyone). Girls need not be watched (they normally stay inside. Ran's text - adults need not be watched.)

Question: Why didn't Rav answer like R. Yochanan?

Answer: Rav holds that the cantillation is also mid'Oraisa:

(Rav): "Va'Yikra'u b'Sefer Toras Elokim...va'Yavinu b'Mikra"- this is the cantillation;

Some say, this is the tradition of extra or missing letters.

Kesuvos 105a (Rav Yehudah): The judges who made decrees in Yerushalayim received stipends from Terumas ha'Lishkah, 99 Manos in all. If they were unhappy with this, they received more.

Objection: Were they Resha'im (who take more from the Tzibur than necessary)?!

Correction: Rather, if this was not enough, they received more, even if they didn't want to receive more.

Bechoros 29a: If one cannot find a Rebbi to teach him for free, he should pay to learn - "Emes Kene". He should not say 'just like I had to pay to learn Torah, I will charge to teach', for it says "...v'Al Timkor."

Rishonim

Rif (Nedarim 12a) and Rosh (4:4): We asked that just like "Limadti Eschem Chukim u'Mishpatim ka'Asher Tzivani Hash-m" obligates teaching Medrash for free, it should obligate to teach Mikra for free! Rav answered that one may receive wages for guarding the Talmidim. R. Yochanan answered that one may receive wages for teaching the cantillation.

Yerushalmi - Suggestion: "Limadti Eschem..." - perhaps one must teach also Mikra and Targum for free!

Rejection: "Chukim u'Mishpatim" must be for free, but Mikra and Targum need not.

Rosh (ibid.): The Yerushalmi permits Sechar Betelah (compensation for what he could have earned in the time he was teaching) even for oral Torah.

Ritva (on the Rif, DH u'Melamdo): Chachamim paid from Terumas ha'Lishkah received Sechar Betelah.

Rebuttal (Rosh Bechoros 4:5): They were paid even if it was not clear Sechar Betelah (it is not apparent how much they could have earned in that time). Rather, since those Chachamim spent all their time judging (or teaching) and had no time to earn money, they had to be paid to be able to eat.

Ma'adanei Yom Tov (5) It was not clear Sechar Betelah, for if they needed more money they would get more.

Rambam (Hilchos Talmud Torah 1:7): If the local custom is for teachers of children to be paid, one pays the Rebbi for his child. One must pay for his child to learn all of written Torah. Where the custom is to be paid for written Torah, this is permitted. However, one may not be paid for teaching oral Torah - "Limadti Eschem..." If one cannot find someone to teach him for free, he should pay - "Emes Kene". One may not teach for pay - "Al Timkor". This is even if he paid to learn.

Beis Yosef (YD 246 DH Makom): Even though adults not need be guarded, the Rambam does not distinguish between adults and children. This is because the Halachah follows R. Yochanan against Rav.

Beis Yosef (ibid. DH u'Mah she'Chasav u'Lelamed): The Tur brings the Heterim of wages for guarding and for cantillation. Nevertheless, he agrees that the Halachah follows R. Yochanan (i.e. R. Yochanan agrees that one may take wages for guarding children. He teaches that one may also take wages for teaching cantillation to adults.)

Poskim

Shulchan Aruch (YD 246:5): If the local custom is to be paid for written Torah, this is permitted. However, one may not be paid for teaching oral Torah. If one cannot find someone to teach him for free, he should pay. Nevertheless, he may not teach for pay. Nowadays people teach everything for pay if they have no other income. Even if one has other income, he may take clear Sechar Betelah, i.e. he abandons business entirely (in order to teach).

Rema: One may take wages for teaching anything enacted by Chachamim.

Source (Hagahos Maimoniyos Hilchos Talmud Torah 1:5): Rav did not allow taking wages for the cantillation because he holds that it is mid'Oraisa. R. Simchah learns from here that one may take wages for teaching anything not given on Sinai.