Wojciech Szczesny is the cheekiest child in the class. He always has been and, if Arsenal's Champions League press conference before the vital home tie against Borussia Dortmund was any guide, he still is.

When Arsène Wenger answered questions in fluent German, Szczesny, seated alongside the manager, put his chin to his hand, pursed his lips and nodded sagely. And when Wenger spoke of the goalkeeper as being "humble", he performed a comedy double take.

Szczesny has an addiction to mucking around; to stealing scenes and barging on to centre stage. In the recent games at home to Marseille and at Norwich City, when he was on the fringes of the action, he performed Cruyff turns to beat opposing players outside his area. There was the sense that he was merely amusing himself.

The Poland No1 is no barometer of Arsenal's confidence levels, purely because he is always so full of the stuff. He has the priceless ability to shrug off mistakes as if they have not happened. But Szczesny believes that the team's oft-maligned defence has grown collectively in conviction and the foundations are in place for serious progress, which goes beyond the Champions League last 16 qualification that they hope to secure against the German champions.

There has been the feeling that an error is never too far away and the central defender Per Mertesacker proved the point at Norwich on Saturday, when he was at fault for the game's opening goal. Wenger has had to improvise at right-back, in the absence of the injured Bacary Sagna and Carl Jenkinson, while Mertesacker and the left-back André Santos, signed in the summer, are feeling their way into a new football culture. Szczesny, though, pointing towards the fewer goals conceded in recent weeks, argued that the work in progress was coming together.

"I feel the improvement," he said. "We work together on the training ground and it seems to be working during games. We are much more confident, we concede less goals and I hope we can keep it going. We got clean sheets in the last two Champions League games against Marseille and that gives us confidence for Dortmund."

The Szczesny swagger was evident when he discussed Robin van Persie's form. The captain scored another great goal in training on Tuesday but, Szczesny added in a flash, "not against me". He has also revelled in the predictable exchanges with the Poland players in Dortmund's ranks – Lukasz Piszczek, Jakub Blaszczykowski and Robert Lewandowski. Which is easy for Szczesny to say.

"They were taking the mickey out of some of the games that we had at the beginning of the season," he said, with a nod towards the 8-2 defeat at Manchester United. "But they haven't been giving me much stick recently. I am confident we can beat them and so my banter will be better than theirs after the game."

Szczesny shoots from the lip but it would be wrong to confuse his front with any lack of seriousness about his game. "You never think that Wojciech is a comedian when you watch him practise," Wenger said. "You have to be careful as well because people want a quick image of you and it's sometimes a superficial one. He is a deep thinker. You do not play at this level and make the decisions he makes if you do not think about the game. When you are honest, you can sometimes look a bit cocky but he is not. He is just honest."

"People still say I am over-confident," Szczesny said, "but I am a big critic of myself. We analyse every little mistake and I try to learn. There is a lot of room for improvement."

There was an amusing moment when Wenger was asked whether Szczesny was crazier than Jens Lehmann, his former goalkeeper. Not a chance, to paraphrase Wenger, who argued that Szczesny was "not crazy". And so to the questions about the 21-year-old's school days.

Did he get into trouble with the teachers? "Yep." Too much chat? "Yep. I have always been this way," he said. "I was born this way."