I would like to particularly (the word <em>specifically</em> would make more sense here) thank you for all that you have taught us through (<em>throughout</em> would be a better word than through, but either works) the whole semester, which is (you should write <em>all of which was quite significant</em> instead of <em>which is...)</em>, quite significant. I am immensely grateful for such (replace <em>such</em> with <em>for all of the)</em> energetic and fulfilling lessons you essentially (essentially doesn't make sense here) teach (taught, not teach since you're talking about the past) us about the powerful vikings roaming all over earth, The (the shouldn't be capitalized) gruesome kindof (no need to put the words <em>kind of</em>) Black Plague and so much more. It contains my sorrow seeing you leave {school name} after all the things you taught students and especially Grade (don't capitalize <em>grade</em>) {number}.
