From a purely academic standpoint, Gatto's 'research' is risible. He uses the classic approach of the demagogue with a point to prove; using statistics from different samples and time frames, generalising from specific studies (even when the authors have specifically stated that this should not happen)and inferring simple, linear causal relationships where many uncontrolled factors are in play. I'd expect (and get) better from one of my undergrad students.
I'm lucky, I have access to libraries and databases where I can chase down the sources of Gatto's ideas. I did so after reading his two latest books. He's about as credible as Goleman on Emotional Intelligence, i.e. not credible at all, really.
Tim