The author is referring to the quote four paragraphs before this one which ends "...teachers need to become ever more skillful in their ability to evaluate teaching situations and develop teaching responses that can be effective under different circumstances".
After discussing this for three paragraphs he then reaches the one you have asked for help with:
“Under different circumstances” is a telling phrase because it challenges the contained setting of the classroom. [i.e. it is challenging for teachers to bring about certain, or different circumstances in a standard classroom setting, to meet both the demanding curriculum expectations and the needs of more diverse learners which he mentions earlier.]
It challenges the comfort zone of those who know telling those who don’t know. [It challenges the teacher's standard methods of teaching.]
It opens to scrutiny the nature of behaviour settings and “construction sites”. The former refers to the conditioned response of human beings to the physical environment in which they find themselves. [i.e. It opens to scrutiny the nature of people being conditioned to behave in certain ways in classroom settings.]
The latter refers to ways in which intelligence is “constructed” by the places and people whom we congregate with, who either constrain or enhance desire and determination. [i.e It opens to scrutiny the ways in which learning is "developed and influenced" by the places in which we live or work and the people we mix with or who teach us. All of these factors can either restrict or enhance our desire and determination to learn.]
Others may be able to summarise it more succinctly, but I am trying to capture the spirit of the original.
Student or Learner