It is challenging to answer questions of what is best to do, as most of Choshen Mishpat (monetary law) deals with rulings of one’s rights and outright obligations. However, we cannot ignore such a noble question. We will present halachic background, and you should know better than we how to act best in your case. Should a disagreement arise in the future, this response, which is based on partial information from one side, cannot be used to bolster either side.
There are a few Talmudic precedents that deal with a worker who was hired for a job that became (partially) superfluous. If, based on the case’s particulars, one side can anticipate the change, he is responsible to stipulate what to do should that occur. If he fails to do so, he is at a legal disadvantage.[1] In this case, it seems that it was stipulated that the school would pay you even if there was no longer a need for twelve hours of work, as has happened and they are doing. However, in the gemara’s parallel cases, there are two things the employer can do to minimize the loss of having to pay for work he does not receive. We will now discuss for your consideration whether either is appropriate for you.
Halacha recognizes that part of a worker’s pay corresponds to the toil he has to put into the job. Consequently, in a case where a person gets paid without having to work, his salary is reduced corresponding to the toil, and he is paid as a po’el batel (an idle worker). The gemara[2] points out that some people do not like being idle, in which case there is no salary reduction.
The gemara,[3] discussing a worker who is paid daily and who finished the job before day’s end, says that the employer can instruct him to do other work during the remaining time if such work is not more difficult than the work for which he was hired. There is even an opinion that he can give the worker harder work if he pays for the extra effort.[4] Another option for the employer is to give him work on someone else’s behalf, thereby obtaining some compensation.[5]
Thus, the school could plausibly ask to reduce your salary to that of a po’el batel or ask you to do other jobs in your spare time if they are not more difficult. (Difficulty may not be limited to exertion but could include factors like embarrassment about doing things which people of your professional standing are not accustomed to do.[6]) The proviso of being paid for twelve hours of therapy might preclude these possibilities, as might the standard professional practice, which is a crucial factor in commercial agreements. You are in a better position to ascertain the matter than we are.
It is likely that by having remained silent and having paid you normally, the school has relinquished its rights (mechilla) to the above remedies up to this point.[7] (In order to use the logic of mechilla, you need to know that someone of sufficient authority is aware of the situation and accepts it.) However, if you want to be particularly noble, you could consider volunteering to either reduce your wages a little or help the school in other ways.
It is logical to say that this case is different from the gemara’s discussion of uncompleted work. Here, you continue to work at your job, just that you have more free time than expected.[8] There is reason to suggest that under such circumstances, the legal, and perhaps the moral, obligation to take a cut in salary or take on additional responsibilities is diminished. Much depends on the extent of the reduction of your workload.