We attend therapy diligently, but I can't see the effect. Does it really have meaning? How long should we continue?

Not seeing an effect is worrying. In common: developmental change is slow, and security, motivation, and small buds are often growing before visible "did it." Looking back in units of a few months with records or photos makes changes easier to notice. About effect and continuation, it's fine to ask the provider concretely about "the current goal," "how it's evaluated," and "when it's reviewed." What the family decides: how far and how long to continue can be reviewed with the child's state and your views. A guide: "is the child attending without strain?" "are goals shared?" If it feels unsuited, reviewing the content or setting is also a positive choice.