Remember those English diagramming classes everyone hated? I'm not very familiar with the education system in Japan, but I doubt they have diagramming classes. In Japanese, the diagramming is built into the language. You tag the subject, the direct object, the indirect object, etc. Everything gets markup. Which part of the sentence is the direct object? Uh... the part with the direct object tag hanging off it? Correc…
I never had the pleasure of taking them myself, butI'm pretty sure Japanese grammar classes are not so fun as you imagine. Putting aside that the norm in Japanese school is rote memorization and pedantic attention to details (e.g. you'd memorize dates of historical events), the Japanese grammar that is taught in class is traditional Japanese grammar. It's pretty streamlined compared to the abomination that is medieva…
The trick for wa/ga is often just to remember that subjects are often implied in Japanese and missing from the actual text/speech. So, "Nekko ga suki desu" because the "watakushi wa" was implied.