A child was expelled from school because he was regularly destructive to school property. An askan advocated for the child, but they refused to readmit him unless someone guaranteed to pay for whatever he would break.
Q: Would such a verbal commitment be halachically binding?
A: Poskim discuss a similar question that could serve as a precedent. Reuven was considering hiring a young man, Levi, to work in his house but was concerned that he would damage some property. Shimon guaranteed verbally that he would reimburse Reuven if Levi damaged anything. Since Reuven agreed to hire the young man because of Shimon’s commitment, Shimon is liable as a guarantor (Nesivos 315:2). Similarly, the commitment of the askan should be binding. However, there are other opinions that would not obligate him.
A well-known principle is that an asmachta agreement (a conditional commitment that is dependent on a future event) is not binding. Since at the time of the commitment it is impossible to know whether the party will have to fulfill it, it is assumed that he did not fully commit and thus it is not binding (C.M. 207).
An exception to this rule is a loan guarantor who is responsible to repay the lender even though at the time of his commitment it was not known whether he would become liable to repay the lender. The guarantor’s liability is in consideration of the benefit he received from the lender. The lender’s willingness to extend the loan was due to his trust in the guarantor; in recognition of being deemed trustworthy, the guarantor unconditionally commits to repay the loan. For that reason if someone commits to guarantee a loan after it was issued, the commitment must be ratified with a kinyan to make it binding, since in this circumstance the lender did not rely on the guarantor to issue the loan (C.M. 129: 1-2).
Some Poskim contend that when the guarantee is itself an asmachta, it is not binding. For example, Reuven sold property to Shimon without a guarantee to reimburse him if the land is repossessed, and Levi offers Shimon that guarantee. Since Levi’s commitment is conditional on someone repossessing the land, it is not binding (C.M. 131:9). This is fundamentally different from a loan guarantor. On one hand, Levi’s commitment is conditional on the borrower defaulting on the loan, but on the other hand at the time of his commitment the borrower became responsible to repay the loan and the guarantor had the satisfaction of being considered reliable. Consequently, his commitment is not categorized as an asmachta.
In your case, since no obligation is generated at the time of the commitment (even on the damager) and the askan is obligating himself if and when the child will damage, his commitment is an asmachta and he is exempt (Gra 131:19; Beis Ephraim, C.M. 34; and Beis Yosef). But other opinions do not make this distinction (Tur, C.M. 131; and Sma 131:18).
Since the matter is subject to debate, if the school wants the askan’s commitment to pay for any damages they would have to draft a contract that would remove the asmachta element of the commitment.
However, if the school insists that the father commits to pay for damages caused by his son, it would be binding without having to draft a special agreement, since that would represent a binding stipulation to the agreement of their relationship (Ketzos 315:2).