About 200 pupils and staff at Teign School in Kingsteignton contracted latent TB, the form of the disease is not infectious.
Ten more people went on to develop the more serious, active form of TB.
Public Health England (PHE) said screening would take place sooner if there was another outbreak.
August 2014 Former Teign School pupil from overseas is diagnosed with TB
February 2015 Former classmates tested
March 2015 Second case confirmed
April 2015 Screening starts of years 10 and 12
May 2015 Public Health England confirm 94 latent TB cases and two active cases found
June 2015 Screening starts of entire school, leading to a total of 200 latent TB cases and 10 active cases found
It is believed the infection was brought in by a pupil from overseas, who was ill for several months. He was not diagnosed with TB until he left the school in the summer of 2014.
Dr Sarah Harrison, deputy director of health protection for PHE, told the BBC the disease spread far wider than they expected.
"We think that for one reason or another, this first case was particularly infectious," she said.
PHE had followed national guidelines that restrict screening firstly to family and former classmates.
This meant the remainder of the school's staff and pupils were not tested until later, when 200 of them were found to have latent TB.
Dr Harrison said: "We have got a small number of people with active TB and yes, if they had been tested they may well not have developed active TB.
"It's easy to see that different stages could have been done a bit quicker, and I think certainly for an infectious teenager we would be expecting things to happen a bit more quickly than they did."
Watch BBC Inside Out on BBC One in the South West at 19:30 BST for more on this story.
Health experts who worked to contain a tuberculosis (TB) outbreak in a Devon school say pupils could have been screened more quickly.