Parents dropping their young children off at Jessons Primary School, in School Street, Dudley, had been left shocked after the incident on December 9.
Officers were called multiple times just after 9.10am after reports a man was using a machete to hit a car windscreen. A mother and her daughter were inside the car.
But a second man, also age 20, handed himself into a police station this morning and has been arrested on suspicion of criminal damage and possession of a bladed article.
He is currently in custody for questioning.
A woman's car windscreen was damaged during the attack.
The investigation continues and anyone with information is asked to contact police via Live Chat or by calling 101. Quote 20DY/305719K/20.