Another complication is an issue I referred to on this forum last year when I reprinted a section from a Scottish office memo which showed that civil servants had already pre-determined by if my memory is accurate 1975 or so , problems with continuing to strap girls ,in that equal opportunity legislation was seen under Scottish law to either lead to more girls being strapped ( politically unacceptable) or to full abolition, which the Scottish Office accepted as the preferable course.
There were a couple of research departments who did try to establish the link, not , in my mind convincingly, but these relies relatively uncritically on international especially US data and studies, ( many of which involved home and school discipline). Which data you accept depends on your stance, as I said on another thread yesterday , on your degree of acceptance of the empiricist method .