English Verb Tense Question

I teach freshman composition at the college level. I have a student who will not let this go. I assigned a critical thinking exercise in which they have to write a paragraph using words of only one syllable. This student insists that --linguistically-- English verbs that form their past tense with -ed are one syllable words. Since I teach composition and NOT linguistics, for my own edificaton, how many syllables do they have -- linguistically. I remember from a course I took that the dictionary and linguistics do not always agree.

[Tdol]

It depends on the verb:
lived = one syllable
acted = two syllables

I don't agree with the student's claim- it depends purely on the pronunciation to me.