During swimming, it is highly likely that water may enter a person’s throat. It is not swimming itself that invalidates the fast, but rather the entry of water into the throat.
If the swimming lesson is compulsory, solutions such as obtaining permission for the days of Ramadan should be considered. If this is not possible, alternative measures that do not compromise the fast should be pursued, such as attending only the theoretical portion of the lesson, refraining from entering the water, or, if entering, avoiding positions that may lead to swallowing water.
In practice, many schools show due regard for religious sensitivities and develop alternatives. Therefore, one should be persistent in seeking accommodation. Nevertheless, hypothetically, if the child enters the pool, swims, and unintentionally allows water to enter the throat, the fast is invalidated, and one day must be made up after Ramadan.