I rarely skipped math lectures in university (only when the prof was really bad; but then I watched video lectures taught by a different prof from a previous term).

The lectures in the hardest math classes I took did not feature any “working through problems.” They were 50 minute pedal-to-the-metal proof speedrun sessions that took me 2-3 hours of review and practice work to fully understand. I don’t know how anyone can see a lecture like that and not see it as an inefficient note delivery system.

I did have math classes where profs worked through problems but those were generally the much easier applied math classes. Those were the ones I least needed to attend lectures for because there you’re just following the steps of an algorithm rather than having to think hard about how to synthesize a proof.

For language learning it’s hard to beat full immersion. When we learn our first language (talking to our parents as children) we don’t learn it by theory (memorizing verb conjugations), we learn it by engaging the language centre in our brains. I think language classes are more useful if you want to learn to write and translate in that language, where you need a strong theoretical background. If your main goal for language learning is being able to speak with loved ones or being able to travel and speak fluently with locals, then sitting in a classroom listening to a lecture seems like a very difficult way to do that.

I meant "problems" in a broad sense -- I loved disorganized professors who would pause and stare at their lecture notes in silence for a minute, realize their proof or example contained some flaw, and then have to correct it on the fly.

I found those moments really valuable if course-correcting was non-trivial -- the typical Definition-Theorem-Proof-Example format certainly is essential for organizing one's thinking and communicating new math in a way that's digestible to other mathematicians, but it is not how mathematicians actually think about math or solve novel problems

In the grad analysis sequence this "course correcting" mechanic was built into the course, since we were required to regularly solve a challenging problem and then present its proof to the class and withstand intense questioning from both the professor and peers. If you caught an error in someone's proof and could help the presenter arrive at a correct proof, you'd both earn points.

The thrill of surviving an incredulous "Wait a second..." from that particular professor (who later became my research advisor) was hard to beat

Anyway my intent was to analogize math lectures (whatever they might look like) with language courses or immersion in the sense that they are an opportunity to practice speaking and listening, and to immerse yourself in cultural norms. I think it goes a bit deeper than this, in that language is inextricably connected to most thought and vice versa -- we experience this in a very explicit way whenever we find our thinking clarified in the process of formulating a question, but it's always there

That said, pure immersion for language learning is actually easy to beat -- lots of research shows that immersion together with explicit grammar instruction has far better learning outcomes than immersion alone. Immersion alone misses lots of nuance -- and it relies on the speaker being acutely aware of the difference between their output and target forms.

With your verb conjugation example, lots of time can be saved by knowing that there's a thing called the subjunctive and that it is distinct from tense and it shows up in a myriad of places tending to concern hypotheticals

Similarly, I gain a lot from talking to mathematicians and attending conferences. But I also need to spend time alone consulting relevant theory, reading papers, and playing with examples. Both are important, but in math it seems you one get away with less immersion

I consider the value in math lectures to come from the speaker’s explanation of why to expect certain things. Is this an obvious fact in another context, rewritten for this application? Is this a surprise? What reasons besides the rigorous argument are there for believing the theory?

A lot of the theorems I learned in school weren’t particularly amenable to intuitive explanations like that.

For example, take Galois theory. The fact that a polynomial’s solvability by radicals depends on the solvability of its Galois group is surprising and not intuitive at all. The fundamental theorem of Galois theory is a very technical result utilizing purpose-built mathematical structures that were developed specifically to study the solutions of polynomial equations.