A student teacher now faces charges of having sexual contact with a student at Tempe Union High School.
But should the district have let him be in one of their classrooms in the first place?
Our ABC15 investigation uncovered teachers in the same district had warned administrators about Joel Calderon's alleged inappropriate conduct years before when he worked at a high school just three miles away.
About three years ago, Calderon started his teaching career at McClintock High School as a math aide.
According to documents obtained by ABC15, the first red flag came up in March of 2010.
In a letter, the school principal warned Calderon not to take students out in his car or to dinner. Despite those warnings, the problems continued in November.
"He didn't heed that information the following fall semester, and it was reported again, that there were some oddities, if you will in his performance," said Kevin Mendivil, Assistant Superintendent for Human Resources with the school district.
Administrators kept a paper trail, writing Calderon was getting too close to some students.
The McClintock High School principal reported Calderon walked a female student down the hallway, and also came to a teacher's classroom to visit her.
Another time, school officials said Calderon was overheard asking a female student if she was "lonely" while she waited in the reception. Documents show he allegedly said she could come down to his classroom "anytime."
According to school documents, when the principal approached him again "he shrugged and said he didn't think it was a big deal."
"There's a fine line you cross. That was addressed in his performance appraisal, which resulted in his termination by the administrator," Mendivil said.
He was fired from the school district December of 2010.
But a few years later at age 26, he was back in the school district as a student teacher at Tempe Union High School just a few miles away.
We asked how that happened.
"His name was sent out along with probably 200 others in the district. And we simply do not have a database, an electronic database by which we can cross reference previous employees. It's just not there," Mendivil said.
Police documents show Calderon allegedly met with a 16-year-old student outside of school and had a few sleepovers that led to oral sex.
Medivil says Calderon passed student teacher background checks by Arizona State University and had a security card from the Department of Public Safety.
We asked if administrators ever recognized his name from the past issues Calderon had with the school district. Medivil said they did not.
Still, his documents remained on file with district, and they did not take a look at them until after this alleged relationship with a student was brought to light.
"But still being in the same school district, can you see as a parent if I'm looking at this that I would be concerned?" asked ABC15.
"Absolutely. Absolutely. And our first and foremost priority is to ensure the safety and well-being of all our students," Medivil replied.
Medivil says because of this case, the district has started manually cross checking its personnel files with applications for student teachers, interns and volunteers.
"There's always something to learn from in these situations, and it just re-emphasizes the need to continue to continually check on the measures that we have in place and the systems we have in place," Medivil said.
The school district maintains all policies were followed when it comes to this case. Medivil says the district now has checks and balances in place so it doesn't happen again.
ASU won't comment on the status of Calderon in the student teacher program at the university.
Calderon pleaded not guilty to six charges of sexual conduct with a minor. He will appear in court on January 30.