A textbook I'm using to refresh some basic grammar states that indirect objects can be identified by it's answering of questions such as 'to whom', 'to what' etc. (fair enough) and they always come before direct objects in a sentence (this raises questions for me).

So the text would identify the pattern in:

The teacher gave the students homework.

as: S - TV - IO - DO

but the pattern in:

Tim kicked the ball to Ken.

as: S - ITV - Prep.

It's been a while, but I was taught the direct object received the action of the verb and the indirect object received the direct object, and also that a verb's classification of transitive or intransitive arises from how it is used in the sentence (i.e. it's not intrinsic to the word itself). So that I would have identified the second example's pattern as:

S - TV - DO - IO

because the preposition is receiving the DO and therefore is the indirect object.

Since 'kicked' can be used with or without an object (i.e. The baby kicked.) I let it pass thinking the text and I could both be correct. But a third example from the text has me questioning how transitivity is assigned:

Problems led to desperation.

the text again gives the pattern as:

S - ITV - Prep.

But, 'Led' is almost never intransitive - not unless it's the answer to a question or given some additional context. And so this classification seems more forced to me.

The text seems to be implying that the role the verb plays in the sentence depends on how you classify the thing it is acting on and that prepositions can not be indirect objects (despite receiving the direct object as well as answering the question 'to what').

Could someone please clarify, illuminate, or otherwise help me make sense of this?