A person with an average intelligence can never be educated to become a scientists, programmer, or an engineer.
Bullshit. You can train a monkey to do these things, even if it takes a while. It is true though that they won't be a brilliant scientist / engineer / programmer they can still be competent to do research ( and understand ) work at various lower levels.
And measuring intelligence is extremely difficult. Someone who is street smart, but didn't finish High School ( and maybe could even score extremely high if they had access to more education while getting by in the world), probably wouldn't score well on a test measuring how much you have learned. Yet that street smart person would likely be able to look at an experiment and see where real world interactions would be happening, and even explain what is going on... all without knowing the technical terms and what the designer of the experiment is actually doing ( on the learned level).
In a similar vein - someone who is extremely good at rote book learning would score really well on the IQ test, but be completely worthless in the real world because they just plain can't read and learn what to do in every single different situation. They may be good at solving the various bits and pieces of a problem, but then someone else has to come in and put everything together into a cohesive whole.
As an anecdote, and even a car one for /. , one of the absolute best mechanics I have ever met couldn't even read. Despite that, you could take your car to him and he could tell you exactly what was wrong with it, tear it down, and rebuild with the replacement parts even if he had never worked on that specific model / type of car. I would call that having a high specialized intelligence, even if there was no way he would score even close to average on a standardized test ( can't read the test = can't do the test pretty much).