My take is that kids today are no less intelligent and no less capable of learning than their predecessors. What's changed in this country is our definition of what constitutes an "education." As others have pointed out here, there was a time when a high school education was truly an effective education, and not just what it has become today -- a bare minimum "credential" that means nothing except that its holder had the patience to spend 12 years in a public school.
We are going to continue to have these debates until we, as a society, get serious about what "education" means and how we go about promoting it among our citizens.
I graduated from high school in 1959. The only reason I didn’t flunk algebra and geometry was because my aunt was a big shot in the order of nuns that taught us. I loved Latin, history and lit. I went to college on my GI bill and graduated magna cum laude. I excelled in French and geology. In my 70 years I can’t think of a single incident in my life where I’ve needed algebra. I use arithmetic every day.