it has nothing to do with singular, it has to do with context and verb moods -- i.e. subjunctive vs. indicative verbs, etc. In this case, "were" would be the subjunctive mood of the verb "to be" and is appropriate for cases in which you are referring to something that's not likely to be true, reminiscing, etc.
I.E. "I wish I were a rich man" vs "Yesterday, I was rich" -- "was" is the indicative mood of the verb and is appropriate for things that are true, or likely to be true in hypothetical situations.
Doesn't anybody know English anymore???
Now, if teaching a class on spanking is something you are likely to do, then perhaps "was" is appropriate
To answer your question, unfortunately, very few know English these days. Carry on.