I've been dipping in and out of the research for decades. Way back when, it appeared the scientific consensus that stuttering was purely psychological. Now over the years, I've watched that be replaced by different thinking. It now appears the consensus is a mix of genes, environmental factors, physical differences and psychological. I think the most interesting scientific research about stuttering is that after so many decades of intense research into stuttering by countless experts and researchers, they still don't really have a definitive clue what causes stuttering.