The Special One (The Outer Limits)

A man confronts Mr. Zeno, a mysterious educator who seems to have alienated his son's affections.

Roy Benjamin and his wife, Aggie, are delighted, but puzzled when they meet Mr. Zeno, who explains that he is a government educator sent to cultivate the mind of their gifted son, Kenny.

Kenny now has super-human knowledge, and even possesses a few mental powers, having seemingly become loyal to the alien.

Nonetheless, it is revealed in the end that Kenny knew of Mr. Zeno's plans since the beginning (Zeno having believed children to be more easily impressionable and more gullible than adults), and decided to feign loyalty in order to better thwart them.

Managing to render the alien powerless by using the sound-wave-powered weather machine against him, removing the essential element from the atmosphere that would enable his kind to survive on Earth, Kenny forces Mr. Zeno to retreat back to his homeworld, Venon, thus ruining the alien's plans of conquest.