Maybe he means that the left has over-interpreted the "suspensions are counterproductive" results (which, honestly, aren't as clean-cut as one would hope) as "strict classroom management is not important", even though classroom management that achieves few disruptions is associated with superior student outcomes (again, honestly, not as clean-cut as one would hope)?

The rhetoric does seem to me to trend that way, though I think David has a bit of work to do to tie it together into something convincing.