Experiments have proved that children can be instructed ____ swimming at a very early age.
Note: Besides “in,” are there other preposition that would fill inside the blank? Thanks
Does it sound right to say "experiments have proved that children can be instructed TO SWIM at a very early age"?

Question

Answer

I can't think of any others that would fit.
To me - 'instructed to swim' sounds wrong. Whether it is incorrect, or just pretentious, I'm not sure. 
I would say 'taught to swim'.
(The 'instructed in swimming' sentence actually sounds silly to me. Infants could also be instructed in quantum physics. The sentence doesn't say that the instruction actually achieved anything!!!)