1 2 3
OK, I've joined them all up. If they are in the correct order, though, it will be a miracle!
I sent a letter about this question to Margaret L. Benner, director of Writing Support Program, English Department at Towson University. And the following is her answer. I think this will be of much help to us about my question.

1. The greater the expectation placed upon people is, often children or students and employees, the better they perform.

2. The greater the expectation placed upon people, often children or students and employees, the better they perform.

3. The greater the expectation placed upon people, often children or students and employees, is, the better they perform.

Sentence #2 is the clearest, "sleekest" sentence among the three. Sentence #1 is awkward because of the placement of the verb "is" before the appositive; sentence #3 also reads awkwardly simply because of the inclusion of the unnecessary "is."

I can't give you a grammatical reason (other than the verb placement in #1) for my choice of sentence #2. It is a matter of typical usage.

I hope that this information helps.

mlb

Margaret L. Benner
Director, Writing Support Program, English Department, Towson University
Online Writing Support Website www.towson.edu/ows, Winner EduNET Editors' Choice Award, September 2007
Linthicum 201B

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I believe that I already said that.