Charlene Ellis, 18, and Latisha Shakespeare, 17, who were killed, and Charlene's twin sister Sophie, who was injured, were studying art and design, and Mr Grayson paid tribute to the "lively, popular and well-liked" girls.
He told The TES: "More than 300 people signed the book of condolence on Monday, the first day back after the shootings, which shows the strength of feeling throughout the college."
Latisha was shot four times and Charlene three times by a sub-machine gun. Charlene's twin sister, Sophie, and their cousin, 17-year-old Cheryl Shaw, were also hit by the bullets at a party in Aston.
Mr Grayson said: "It's not impossible that there are groups in this college who know about what's going on (in the gangs). But within the college we monitor behaviour according to our ethos and we have never had any incidents with knives or guns."
Grahame Murray, head of Sacred Heart Catholic primary school, less than 100 yards from the scene, said: "The shooting of these girls highlights a feature of life around here. No pupils at my school have any links to what happened, but some have relatives in their extended families who are involved in gangs or who have been shot.
"Like many schools, we are very aware of what's going on in the streets - but we can't let it take over our everyday lives."
Sir Robert Dowling, head of George Dixon International school and sixth form college, said: "Children are living two lives: life in school, which they see as a haven, and life out there where they are afraid of running into these gangs. Sometimes staff have to confront the violence at the school gates, but it has never spilled into the school."
Meanwhile, black community leaders are calling for reformed gangsters to warn children in inner-city schools about armed crime.