by: Rabbi Yechezkel Khayyat
The Gemora introduced the concept of workers who carry heavy bundles. Since they need to stay in shape for such strenuous work, when they are idle, it is a loss for them, and therefore an employer must pay them full wages even for idle time.
The Rosh (3), as well as other Rishonim, apply this to Torah teachers. If one hired a Torah teacher for his son, but the son fell ill, the employer must pay the Torah teacher his full wages. When a Torah teacher does not teach, this leads him to forget his knowledge, and not be as sharp as when he is teaching. Therefore, idleness is a loss for him, and he gets paid full wages.
The Ashri Notes questions this Rosh, and states that if the teacher is not employed to teach, this does not preclude him from still learning, to hone his knowledge and intellectual skills.
However, the Pilpula Charifta (10) explains that the work involved – and consequent sharpening of knowledge and skills – increases when one has a student, compared to one who learns on his own. If the employer can provide the teacher with a similar student, he must teach him, but if he does not, his own personal learning does not adequately replace the loss of not teaching.
The Tur (HM 334) rules like this Rosh. The Shulchan Aruch (HM 335:1) also follows this Rosh, but the Rama adds that if the court sees that this teacher is pleased by not having to teach, he is not paid his full wages.