Your instincts are better than you think. The problem lies with the idea of ‘stative’ contexts and verbs. There are several perfectly good ways of phrasing the proposition:-
- I entered the classroom and I expected to see ...
- I entered the classroom and I was expecting to see...
- I entered the classroom expecting to see ... (this is a neater version than the other two)
- As I entered the classroom I was expecting to see ... (this brings out the fact that the act of entering and the state of expecting were simultaneous)
The problem was that you had stumbled into the quicksands of English verb tense from which few learners of English (or teachers of English) return: I mean the difference between the so-called continuous present (or, in this case, past - I am/was writing my daughter a letter, representing something I am/was actually doing now/then - and the repetitive/habitual present - I write my daughter a letter once a month, representing something I do regularly, but not necessarily or only at this moment. The French use the same tense for both is these senses. If it is vital to make the difference clear, they will say “je suis en train d’écrire...” “I am in the process of writing...” or something like that.
So someone might say, “OK, now I am thinking I am understanding the difference”. Wrong again! He has just marked himself out as a foreigner. This usage with -ing is the first thing an English speaker will notice.
So the writers of grammar books look for a simple rule that will help people trying to get hold of this tricky distinction between two forms of present. They tell you that some verbs are static or stative or state verbs, and that think and understand are two of these. The grammar book will provide a helpful list of the verbs to look out for, which you can learn. This will help up to a point. But English speakers love to disagree with other English speakers and will argue furiously over whether this or that verb expresses a ‘state’ and so should be on the list
I am one of them. I can see that expecting is a sort of mental state. But that does not prevent the correct use of ‘.. am/are/is or was/were expecting’ in certain contexts. I offer a perfectly good use in the following little dialogue.
A: I’m off to town for a coffee. Are you coming?
B: No, I can’t: I am expecting a parcel delivery.
This does not show that expectation is not a mental state. It obviously is. But the rule about state verbs and lists of state verbs are insufficient.
For example, belief is obviously a mental state, and so you shouldn’t, on the state verb rule, ever say “I am believing you.”. You should say: “I believe you.”
Normally, that’s right. But we can say (threateningly): “I’m believing you, but I’d better not find out you’ve been lying.”.
Of course (of course?) what the sentence really means is that I don’t really believe you at all: I’m believing you for now. My believing you (or saying I do) is bounded by the present. Similarly I can use ‘am liking...’ where normally we shouldn’t.
I might message my bitterest enemy as follows: “I am reading the news of your forced resignation, and I’m really liking it”.
So rules about ‘stative’ verbs, or ‘state’ verbs, or whatever you prefer to call them are helpful up to a point. But they are only rough approximations to the behaviour of native English speakers. What you are dealing with is an attitude to what is being said. The stated event or action is stated as both in the present and bounded by the present.
In English, mental states are usually treated as not bounded by the present, because we do not like to think of out mental states as in any way temporary. But this is not always so. So stative verbs in the present tense are not usually used in the form ending with ‘-ing’, but sometimes some of them can. Your was one of these.