Step 1: Identify the subject of the sentence.
The subject of the sentence is ``One'', which is singular.
Step 2: Apply subject–verb agreement.
A singular subject requires a singular verb.
Step 3: Locate the error.
The verb phrase ``are missing'' is plural and does not agree with the singular subject ``One''.
Step 4: Correction.
The correct sentence should be: ``One of the boys is missing from the class.''