Son's is correct. "my son's teacher..."
The possessive form of the plural noun sons is sons'.Example: Their sons' names are Mark and Jack.
The possessive form of the singular noun son-in-law is son-in-law's.Example: I'm making a cake for my son-in-law's birthday.The plural form of the noun son-in-law is sons-in-law.The plural possessive form is sons-in-law's.Example: Both of my sons-in-law's birthdays are on the same day.
The singular possessive form of "test" is "test's".
The singular possessive pronouns are mine, yours, his, hers, and its. The singular possessive adjectives are my, your, his, her, and its.
The singular possessive is ant's.The plural possessive is ants'.
Museum is singular. Museum's is singular possessive. Museums is plural. Museums' is plural possessive.
The singular possessive of dish is dish's
Taco's is the singular possessive.
The singular possessive form is classmate's.
The singular possessive is biker's; the plural possessive is bikers'.
The singular possessive is fish's.
Grave's is the singular possessive.