"Él le está dando al maestro una manzana."
Translation:He is giving the teacher an apple.
Mrule: Not exactly.I think it is easier to think of it this way: indirect object pronouns are mandatory when there are indirect objects nouns in the same sentence. Por ejemplo: Juan le da un baso a su bebé. John gives a kiss to his baby. (The LE is mandatory because of A SU BEBE, an indirect object noun.) The indirect object is often, but not always, a person. Look at the DL sentence we are discussing: the teacher is the indirect object noun. In my example, the baby is the indirect object noun. Indirect object nouns are frequently preceded by the personal "a" preposition.
A: I don't know if Spanish people "give a bath" but in English the preposition 'to' is correct when the word order is thus:
He is giving an apple to the teacher.
I am giving a bath to my dog.
She is giving a bath to her baby.
She is giving the report to the boss.
B: Your last example is not the same, as the reports are not given "to" the hour, (I think that "every hour" is an adverbial phrase).
No because 'le' is a 3rd person singular, direct object pronoun, and it needs to be specified who/what exactly is being talking about. If you did not include 'al maestro,' the sentence would say "He is giving he/she/it an apple."
The personal 'a' is required since an object (teacher) is being introduced in the sentence.