When I went through initial training in the US back in 1980, the washout rate was 50% in the facilities after the Academy at OKC. After the strike of '81, that improved to perhaps 70-80% passing.
Since about 2000, in my units, passing rate was around 80-85%, but they were giving those trainees way, way more time to qualify than back in the 1980s. In a busy up/down radar facility, had seen 4 years to qualify before I retired.
Maximum training hours varied up and down depending on how badly they needed people over the last 15 years or so. Also, when I was first hired, most everyone had an aviation background of some sort to qualify for hire. Not so after the strike. Many didn't know UHF from VHF or piston from turbine.
US Southwest region