'Boring' is an adjective here, not a verb, so that can't change. How about: *I sit in boring classes every day. = I sit - present simple * At the moment I'm sitting in the most boring class of my life. = I'm sitting - present continuous

Not 100% sure here but I think the problem you are having is that you are focusing on the wrong verb. Boring is simply describing the class. The action you are doing is 'in'. Subject + verb to be + verb(ing). I + am + in. The problem is that 'in' doesn't work as the verb here. I'm not smart enough to be able to give you a technical explanation, so let me just try to show you an example and maybe someone else can fill in the rest. Lets change 'in' to 'attend' (simple present) I attend the most boring class in the world! (present continuous) I am attending the most boring class in the world! You see that boring doesn't change because it is just describing the class. The important verb is 'attend' we change that from its simple form to +ing for present continuous. We also add the verb to be (am) which we didn't need for present simple.