So there is no suffix on school or preposition to denote that school is the destination. Just something like “her son every day going school is”?
If that is true, then it should have accepted 'their' son as an answer - I understand that they are discouraging non-gendered words as they don't exist much in Hindi compared to English, and 'their' is technically plural, but in English it is used when the gender is uncertain
Agreed, a gender neutral third person they/their is ideal in these situations and actually more natural than the current ad-hoc flip flop between his/her.
It's because non-natives may think that such words indicate plurals which might confuse them further as the sentence end with है not हैं. However, Duolingo should make sure that both his and her are accepted as answers in such questions.