あらい先生の日本語 (Arai-sensei's Japanese) is a YouTube channel where Arai-sensei, a Japanese teacher, teaches keigo and grammar for the JLPT N4 and N3. Arai-sensei's videos consist of him standing in front of the camera with a full lesson written on the whiteboard. He then explains the lesson, writing extra comments and doodles on the whiteboard as he goes.
The main reason I recommend this channel is that Arai-sensei's teaching style is basically plucked right out of a typical language school. He uses gestures and writes kanji with furigana on the board to clarify what he's saying, but his Japanese is still very natural, and he's not slowing down too much. He also uses the Nihongo Sō-Matome textbook.
In true language school fashion, Arai-sensei teaches Japanese in Japanese, without a lick of English in sight. It's excellent immersion, but it does mean you'll have to be able to follow simple Japanese speech.
Anyone who wants free Japanese language school lessons should definitely check out Arai-sensei's channel. Even though it might feel hokey to watch someone film themselves in front of a physical whiteboard these days, it's worth it for the realistic Japanese teaching experience.