I'm the weakest student in language school. How can I improve?

I am Vietnamese, and I'm currently struggling with learning Japanese. How can I apply the immersion method effectively? My school uses the traditional method: vocabulary, grammar, and conversation practice. I'm currently the weakest in the class. I keep forgetting vocabulary, my grammar is all mixed up, and especially my speaking (kaiwa) is poor. I know about immersion, and I've been watching videos, but I don't feel I'm using it effectively. I can somewhat understand the context, but I don't take any notes because I don't know which words are important or frequently used. Many people at school criticize this method, but I don't care much. What I care about is time, because two-thirds of my day is already taken by traditional learning, and I only have the evenings to study. But every time I sit down to study, I get tired and fall asleep. So I don't know whether I should continue both methods at the same time, or just focus on traditional learning first, then switch to immersion later.

There's a couple pretty big problems with school.

In school, youre forced to output way too early and use the skill building approach instead of natural language acquisition. You get stuck thinking in your native language and trying to translate it into Japanese, and that leads to a lot of bad habits. And you know how harmful bad habits can be.

Bad habits in language learning are one of the biggest problems you can run into, because once you've etched something into your brain, once you've built that neural pathway, it never fully goes away. You can let it atrophy, you can build new patterns, and you can switch your default, but it's still an uphill battle. That is one of the reasons AJATT says to avoid premature output and prevent bad habits as much as possible.

The other problem is that you'll be hearing your classmates, who suck at Japanese, speak broken japanese all the time. That's going to be really bad input for you. You might be hearing this bad, broken input many hours a day. You're doing group activities with other people, hearing other people raise their hands and talk, and so on. A lot of your input at the language school is going to be from non-native people who still really suck, and that's bad because you will pick up bad habits from them.

I was once told about this Japanese girl who studied abroad in the US, and her host mom was Indian and spoke English as a second language. This Japanese girl would try to speak English with an Indian accent. Your brain does not know the difference between broken input and native input. It just takes in input and copies it. So you really want to avoid low-quality, non-native input as much as you can.

If you're spending many hours a day, five days a week, in a really bad environment, that is going to have a pretty strong negative effect. That said, it is not going to be completely irreversible, and there are things you can do to reduce some of the damage by getting as much input as possible. At school, you could try to cut down on output, avoid speaking, and maybe even plug your ears when other people are talking. You can probably reduce the harm somewhat, but I don't think you can get it to zero. So you are still going to take some damage from that environment. That is why it makes sense to quit language school altogether.

You mentioned that you keep forgetting vocabulary. It is important to choose the right way to memorize it. In school, they probably use traditional methods like memorizing words and their translations from a list. Instead, you want to use an SRS, like Anki, and make targeted sentence cards instead of isolated vocabulary cards.

I recommend quitting language school, but if you decide to keep going to class for any reason, using an SRS will help you become the strongest student there. Memorization is not unique to language learning. With an SRS, you can memorize anything, including vocabulary and grammar.

Working with the content and trying to understand the unknown parts is very important. If you just immerse by watching videos, like you said, it will not be very effective. You need to mine every sentence with unknown words, or you will improve very slowly. If you are still at a pretty low level, start with simpler content, like slice of life anime.

In general, immersion as a beginner is an intense process. You need to sit down, probably make a subs2srs deck from a slice of life anime, or use MPV to pause and make cards, and go sentence by sentence. Read every word and add definitions for the unknown ones. Pick 1T sentences from the episode and learn them.

You said you do not take notes because you do not know which words are important or used often. First, instead of taking simple notes, put sentences in the SRS. Next, there are two ways to figure out which words matter. You can use frequency lists, but they are usually only reliable for the first 2,000 words or so. Or you can save sentences you encounter in Anki regardless of their frequency, and when you notice you are about to make a card for a target word you already have mined before, just learn that card that day.

I would add most sentences with unknown words to my SRS and let them pile up in my deck. I would not learn all of them right away. Instead, I would pick 10 of the most interesting ones each day. The bigger your sentence bank in Anki is, the better. It gives you a way to quickly find example sentences for any situation.

It is normal for your grammar and speaking to be weak as a beginner. You are just not at the stage where it is recommended to start outputting. First, you need to learn to understand Japanese at a really high level, and then start practicing speaking. You can only acquire grammar by listening to and reading a lot of example sentences where that grammar is used.

Finally, you said most of your day is taken up by traditional studying, and by the time you switch to immersion, you are tired and fall asleep. Immersion is really about doing it all the time, which is why it is called "all japanese all the time." So I think the best approach is to find ways to incorporate immersion into every part of your life, so you do not have to switch between a bunch of different study modes.

AJATT says Japanese is the base. You live your life in Japanese and use other languages only when absolutely necessary. Since passive listening is the easiest, I recommend listening passively while you do everything. For example, you can listen to Japanese at school or while commuting to school. Next, see if you can take notes in Japanese and use Japanese for other school subjects. In your free time, only watch Japanese movies and TV shows, read Japanese books, and visit only Japanese sites, etc.