STAFF at Winterbourne Boys' Academy are to hold a second day of strike action tomorrow (Tuesday).
Eight teachers staged a walkout seven days ago in a row over lesson observations.
The NUT was confident of avoiding further action but Platanos Trust, which runs the school, cancelled talks planned for last Wednesday.
In a letter sent to parents explaining tomorrow's action, the union's Croydon branch said it "sincerely regretted" causing further disruption "especially as it is unnecessary".
It continued: "We were confident that we could have averted further action after some limited progress in the first round of talks.
"Representatives of the new owners had indicated they would respond to some written proposals from the union.
"However, at short notice, they cancelled this meeting without giving a reason and have not responded to our requests for a new date."
Winterbourne Boys' Academy, in Winterbourne Road, is expected to remain open despite renewed industrial action, with staff at the trust's Lambeth school set to fill in.
NUT says teachers have been subjected to lesson observations on an almost daily basis since Platanos took over in April.
The school had been in special measures since failing its Ofsted inspection in October 2012.
The union has been riled by a letter sent to parents by Judette Tapper, chief executive of Platanos Trust, who claimed staff had said "they did not like their work being monitored".
"Teachers value helpful advice following monitoring," the NUT letter said.
"What teachers strongly object to is being unnecessarily monitored much too often, being subject to unfair negative criticism and having opportunities for their professional development withdrawn.
"Teachers would hugely welcome seeing the head teacher and the leadership team teach some lessons, so that teachers can learn from their good practice. Unfortunately, the school leaders won't do this."
