Q. Is it necessary to use a comma after words like next, then, after that, last, and finally when they are the beginning of a sentence? I am a lower-school teacher and need to clarify this.
A. Punctuation is not so simple that you can make a rule that a comma “always” follows a given word or phrase. Commas depend on syntax as well as pacing, tone, and personal preference. Two examples with next:
Next comes the scene where he buries the toenails.
Next, since he was still breathing, she worked a crossword puzzle.
Please don’t teach your students punctuation until you understand this. Find a grammar book and read the punctuation chapter. CMOS is a good place to start.