Bring Sentence Diagrams Back in Full

When I see people in the 12th grade, born and raised in the US, and yet speak and write english worse than I (a former ESL student) do, something just doesn't stick up right. It's not just incorrect past tense ("I should have went"), or the amazing spelling mistakes ("Absolutaly"), it's the lack of any understanding of grammar.

This is a true story from the 9th grade:

The English teacher was going over basics of grammar due to an increase in errors for our grade. On our first grammar lesson for this "catch-up", she gave us what she called to be an easy exercise-which it was.
She wrote a sentence on the board. I don't remember it exactly but it was something simple like this:

"I saw the dog and him".

This part of the lesson was about going over sentence parts. It was supposed to be a 5 minute review so we could go on to real lessons.
So she asked "which is a subject pronounc?" and at first no one answered. I just figured no one wanted to answer. Then! Someone proceeded to answer; his answer was incorrect (if I remember correctly, it was the verb). When he did that, a few people started talking and saying he was wrong and they started giving their own answers. Soon enough, we nearly had everyone in the class giving wrong answers.

I'm internally laughing at my seat. Surely it's "I". I even doubted myself for a second-maybe sentence parts were different here? While I had been in the US since the 6th grade, no class had ever bothered going over sentence parts. The ESL class I was in that year was supposed to have one but then the teacher found out we had all learned sentence diagrams before and instead moved on.
Then the teacher told them all to stop and said the one answer no one had bothered to give out: "I".

Because of the overall lack of understanding everyone had (they really had given just about every answer but that one), our 5 minute brush up ended up becoming a full lesson. That's just sad. We're talking about a 20+ student class and , at the very least, half of the students had bothered to give out an answer. That means at least 10+ students didn't know what a subject was.
I thought and wondered how they couldn't know something so basic. I found out later in my French class. I once had told my teacher that she would have an easier time teaching the difference between Direct and Indirect objects if she would use a sentence diagram. Do you know what she said?

"Yes they would, for a student who knows how to use them. However we don't really cover sentence diagrams much, and the students that do are usually in very low grades that cover only subject, verbs, and adjectives. For me to use diagrams to help, I would have to teach them. That's time I can't waste."
Here's my advice to English teachers.

The key to better writing and reading comprehension:
No, it's not making students write more essays.
No, it's not making them read more books. (Unless they happen to have perfect grammar throughout the entire book).
No, it's not making them learn more complicated vocabulary.
It's understanding of sentence parts.

I guarantee Shakespeare will be a lot easier to understand if a student doesn't go into confused mode when there are inverted sentence parts (aka, if the student can tear apart the weird sentence and reorganize it to something that makes sense. This requires being able to tell apart word categories)
I guarantee people will have a much easier time learning languages, especially roman languages, if they're able to use a grammar rule without first having to figure out if the word in question is meant for that rule.
Also, being able to tell between parts of a whole sentence can help for logic and, by association, math, technology, and music.

Essays and vocab you're supposed to do after the students knows the basics. You wouldn't have someone attempt calculus if they've never learned how to add and multiply right? Why should you skip the basics with English?

As far as book reading goes. Reading books can be a great tool for English. However in contemporary works there are more uses of slang and bad grammar in order to make the characters more real. This is great for entertainment value, but not for English reinforcement. You wouldn't have a child watch a movie where people are shot, and then see those same people come back completely unarmed in another movie without explaining to them the difference between movie death and real life death? Well you shouldn't have someone read bad grammar before they understand the difference between good and bad grammar.

I'm not going to say I'm perfect. I'm not. I make plenty of mistakes. However, "I been saying its better if you want students to read and write good".

Parts of sentence diagrams that are forgotten over time:
Pronouns (and different pronounce types like possessive and reflexive)
Verbs (auxilaries aka helping verbs, roots, verb tenses)
Conjuctions
Objects (direct and indirect)
Articles (yes..those things call "the" and "an" have names too)
Adverbs and Adjectives. They're not forgotten but often confused.
and others I can't think of right now..

When should sentence diagrams be taught?
Basic sentence diagrams (subject/verb/adjective/object) should be in the 1st and 2nd grade.
Advance (everything else) should be in the 3rd and 4th grade.
Reviews of everything should be in every grade until high school. Just a 1 week review at the beginning of the year should do.