It could be truancy, poor reading, difficulties with their homework or bad behaviour. Whatever it is, the teachers are waiting to discuss it. Across the town at Penydre High School the gates are also open. Both schools have launched parent clinics - just one of the measures the town is using to improve GCSE results.
John Williams, headteacher at Penydre, says that the school's results were deteriorating. Two years ago, the proportion of children getting more than five A-C grades at GCSE was just 13 per cent and heading down.
"I realised we needed to raise achievement desperately," he says. "So I established breakfast clubs, homework clubs and study weekends and in two years we have doubled the percentage getting A-C grades. Now we are looking to do it again."
At Cyfarthfa the results are better, but headteacher Alan Pritchard says that he believed there was room for improvement. "I felt we were a good school but we could certainly do better. We had been stuck at 35 per cent A-C grades at GCSE for years and I wanted to improve that when I took over in the early part of last year."
Like his counterpart at Penydre, Mr Pritchard has used the time after school and during the holidays to give pupils extra time to study. He has also introduced a strong reward system to motivate pupils.
These measures have already started to pay off. Cyfarthfa managed 44 per cent A-C grades in 1996, and Mr Pritchard is hoping that performance will continue to edge up every year.
Pupils at the school say that they have noticed a dramatic change in attitude among teachers over the last year. "There is a much better atmosphere in the school and teachers are prepared to concentrate on us rather than think about their own needs," says 17-year-old Sarah Hill.
Her point is echoed by 16-year-old Robert Davis: "Today, teachers are always willing to give up their time to help you but my sister took her GCSEs here two years agoand said it was totally different then."
But he believes that girls are responding better to the new methods than boys. "At the homework clubs there are lots of girls and only a few boys. Our headteacher is trying to turn it into a competition between the sexes to encourage us, but there is still some way to go to persuade the boys they have to work harder."
Last year for the first time, the school linked up with the University of Mid Glamorgan and sent pupils on the borderline between C and D grades for maths GCSE for extra lessons for a week during the holidays.
One pupil who took the course, 17-year-old Cerri Bunce, says that it was an excellent idea: "The course at Glamorgan was very intense, but it allowed us to brush up on all the maths we'd learnt during the year - and it ensured I passed the exam."