Clefairy does not evolve through levelling up, you must obtain a moonstone and use it on it. (There are three moonstones in the game)
lvl 31
It will evolve at level 7.
lvl 28
lvl 18
lvl 25
just train it to a higher lvl!
He evoles lvl 28
You level it up to lvl 36.
give it a moon stone
Ledyba > lvl 18 > Ledian
lvl ten
Magnemite evolves into Magneton at LVL 30.