I was training recruits in the Royal Artillery '64-'65 (Oswestry); in those days the Army tested recruits' intellectual abilities on joining, and graded them from SG (Standard Grade) 1, down to SG 9.
To join the Royal Artillery, recruits had to be SG5 or above. In every training platoon of 40 there would be 10 or so SG5, who were unable to write a brief factual account of how they got to the camp from home, or to add 2 2-digit numbers. The same recruits would be unable to read anything beyond a 2-word newspaper headline. This was all put right by the end of the 8-week course. It was rarely, if ever, the result of lack of intelligence; it was the result of rotten schools and teachers, who allowed some of every class just to "sit at the back" with no encouragement, while they dealt with the more receptive pupils. Overcrowding and lack of funding were also a root cause.
So what's new in 2020? Not much, we still have some poor schools and poor teachers, lack of proper funding, and overcrowding. Giving pupils iPads isn't an answer; it's papering over the cracks.
(To put it into perspective, the infantry regiments accepted recruits down to SG9, but in those days infantrymen were not expected to be intellectuals.)