In this fall, I am going to begin in eight grade (in high school). How would you say ‘I’m in eight grade’? Что лучше, «Я в восьмом классе», «Я хожу в восьмном классе» или «Я хожу в восьмной класс»?
If you’re wondering about the ‘going in’-construction used with ‘grade’, I’m just applying Swedish and German knowledge to Russian, we’ll see how that turns out. ☺
See my comment on cerez00.
If you want to say that he is currently walking to the school, "идти" looks like a better fit for your sentence, so I guess you could translate that as "он идёт в школу (пешком)".
If you say he generally walks to school, I would add пешком to make it clear that it's about going on foot, and not just about going there in general, so maybe "он ходит в школу пешком".
Btw, there are some nice example sentences with these "go"-verbs here.