Or Cooksey had it nailed (almost)
Various researchers over the years have noticed that the adolescent male voice does not "break" overnight, but mutates downwards in discrete steps that correspond to growth patterns during puberty. The most well-known worker in this field was John Cooksey, who died in 2012. His most important work was published in 1977, revised during the 1990s and issued in its final form in 2000. Ron Morris once said to me in conversation "Cooksey had it nailed". My own work has proved this to be so. The boys I have studied have all, without exception, done exactly what Cooksey said they would do. That is a strong recommendation for any scientist!
There are three important caveats:
1. Since Cooksey's death, boys' speaking voices have become deeper than expected for the age norms he gave. I have explored all sorts of possible explanations for this and finally concluded that change in the timing of puberty is the best explanation. The implications for choir singing are considerable.
2. There is a relationship between how closely boys appear to conform to Cooksey's norms and how intensively they sing. I have worked extensively on this.
3. Studies spawned by Cooksey's work have focussed on the growth of the larynx at the expense of growth of the pharynx (upper airway). I believe that has held back our understanding of timbral changes during adolescence and that is the topic on which I am now working.
(The picture was taken during Lockdown when I was not allowed to enter the boys' schools or homes, but the work continued!)
These short videos are based on case studies of boys at each of the main stages of voice change described by Cooksey.