Peter Walker is rushing through the corridors of his school on the way to a meeting - but he can't help tutting over the splodges of chewing gum dotting the carpet.
One might have supposed that would be the last thing on the mind of an acting headteacher brought in at short notice after the previous head resigned on the last day of the summer term, but Mr Walker sees it as symptomatic of broader issues.
"One problem you find in a school where the leadership has been problematic is that things like routine cleaning haven't been happening," he says.
Mr Walker has taken over at Longhill school, an 11-16 comprehensive with 1,100 pupils. He displays impressive dedication to his temporary job - particularly as he is more usually assistant director of education at Brighton and Hove Council.
After studying modern languages at Cambridge, Mr Walker, 46, went straight into teaching and became deputy head of a London secondary school. But in 1988 he became an education adviser - and this headship is his first post in a school for nine years.
He accepts that some staff and parents have been waiting for him to fall on his face since he took charge on September 1, three days before term began.
When he visited the school for the GCSE results in August, he was a little worried, too: builders were working on a Pounds 1.25 million extension programme, not due to be completed until May.
"I thought 'How on earth are we going to open this school?'" Mr Walker says. "We've had to sort out very clear health and safety procedures." Now everything appears under control, with one deputy liaising with the builders each day; but Mr Walker still has a school to run, 14-hour days to work - and sceptics to convince.
"We had a parents' meeting last night to explain the situation and 350 turned up," he says. "I was asked very directly by one parent about what right I had to come here.
"I'm not going to be here long, but what an acting head has to do is have an impact and give some direction. We're due for an OFSTED inspection in the next 12 months - and we're making a fresh start."