"We know that our community will still be feeling the effects of [Tuesday's] events at the college, and we want to thank you for your support and understanding during this time," principal Andrew Savage said in the message.
"As this is an ongoing police matter we do not have any further information to share. Our thoughts are with those who have been impacted by the events."
Because the response from students and staff was so good, they would not be going ahead with a planned drill on Monday, Savage said.
"The safety and wellbeing of our students and staff is our priority and continues to be our focus."
He reminded students that when they came to Tawa College they agreed not to bring anything that could be used to harm themselves or others.
There would be guidance counsellors on site to support students, and supervised spaces are set up for students if they need a break.
"Extra security will be in place to support staff with supervision across the school grounds this week."
Savage asked that all students carry their ID with them, particularly Year 13s who are not required to wear a uniform.
"It is normal to want to know what happened and so there may be lots of discussion."
One student told NZME on Tuesday about the moment the school went into lockdown, saying they had been sitting in class when they were told "go to class, get on the ground, turn the lights off, shut the curtains".
The student, who did not want to be named, said they were in lockdown for about an hour, until 3.30pm.
The school has been contacted for comment.
