Dr. No (1962)
The children of a small town grow suspicious of the area's new psychiatrist after some of their friends are forced to pay him a visit by their parents and teachers after misbehaving in class. Upon returning to school, those who had sessions with the Dr. No are oddly devoid of personality and energy.
Could Dr. No be committing experiments on kids? Or replacing them with clones? There's only one way to find out - pay him a visit yourself