Why are pupils distracted?

Why are puplis unmotivated at school? What distracts them? Why are they being  diagnosed with ADHD (attention deficit-hyperactivity disorder)? Are we, educators, leading them to it? Is it a social problem? Do they have excess of stimuli? Is routinely anaesthetising them with Ritalin the solution?
I am sure we all share the same concerns.
I have watched this video from Sir Ken Robinson which ilustrates these concerns quite well. Have a look.