A 14-year-old was arrested Thursday for making threats to Tincher Preparatory School, making it the fourth school threat Long Beach police have responded to this week.A staff member at Tincher, a K-8 school, overheard students talking about the threat Thursday and immediately reported it, a Long Beach Police Department statement said.A school safety officer detained the teen before Long Beach police arrived and arrested the student for threatening school officials.Thursday's incident came after three separate high schools received threats Tuesday and Wednesday.The first was a threat of a shooting at Long Beach Polytechnic High School that police learned of about 9:15 p.m. Tuesday.According to a statement from the Long Beach Police Department, detectives worked through the night to determine if the threat was real, but ultimately found it was not credible.The statement did not say how they learned of the threat.Then on Wednesday morning, staff at Millikan High School reported a threat made by a 15-year-old freshman that was overheard by his fellow students. The boy was arrested on a charge of making criminal threats.On Wednesday afternoon, a Wilson High School safety officer detained a 16-year-old junior student for threatening harm to others at the school. That threat was also overheard by classmates, the statement said, and that student also was arrested for making criminal threats.Police said the incidents don't appear to be related.Police say there will be increased patrols across all Long Beach high schools, and they encourage anyone with information about a threat to a school to contact authorities immediately.