Other options.

He is huge (and she tells him):

• Miss Love tells him how big he is and starts to worship his cock. He could believe her and go along with it. Lots of fun sex entails or maybe he becomes suddenly more dominant with his new found confidence/belief that that is what "alphas" do.
• Maybe she even invite him back to hers etc He might not believe her and she has to prove it: putting on condoms that don't fit, comparing him to toys/pictures, Jack/someone else might stay back spying/come in (other teacher F/M) or something and get caught and pulled in for comparison etc.
• Other people/teachers could be brought in to "reward" him.

He is huge (and she doesn't tell him):

• She decides to keep this to herself so doesn't tell him how big he is encase he decides to use his new knowledge. Or she decides to tease him for being "small".

He is tiny (and she tells him):

• Sad all round :(

He is tiny (and she doesn't tell him):

• Small penis worship.

He is normal?