Isn't there any student of the same height as Tom in the class if "Tom is the tallest in the class"?

If Jim is the same height as Tom, and other students in their class are not as tall as them, then can we say

Tom is the tallest student in his class.

? Or, Should I say

Tom is a tallest student in his class.

? Or, Should I say

Tom and Jim are the tallest students in his class.

?

Superlative implies one.

Comparative deals with equivalents. (Jim is as tall as Tom.)

With superlatives we always use "THE", which is singular:

THE most or THE least, etc., one single entity of a group. "Entity" can be the one object or the one group of objects.

"Tom is THE tallest." There is no one taller or as tall as Tom.
If Jim is as tall as Tom, then Tom is not THE tallest. Neither is Jim THE tallest.

"Tom and Jim are the tallest ones in the class."

You can say

Tom is one of the tallest students in his class.

or

Tom and Jim are the tallest students in their class.

Saying that

Tom is the tallest student in his class

does somewhat mean that there is no one of the same height.

But you cannot say that

Tom is a tallest student in his class.

• I disagree that saying Tom is the tallest... is correct if there is another of exactly the same height. One could indeed say one of the two tallest.... But superlatives are superlatives and I do not believe they allow for other exact equivalents. Apart from anything else it involves the definite article, which indicates singularity.
– WS2
Feb 21 '16 at 7:40
• @WS2 'Tom and Jim are the tallest.' The superlative may be applied to a subset of order greater than one. Feb 21 '16 at 16:39
• @EdwinAshworth I agree.
– WS2
Feb 21 '16 at 20:29
• Wish I could vote twice Feb 22 '16 at 8:02
• Or "Jim's class". But to be impartial with respect to both Tom and Jim, let's say "their" :-)
– user2505282
Feb 22 '16 at 8:05