Tom Coleman, education convener in Falkirk, said the slight decrease in performance at Standard grade between 1999 and 2002 could be down to evening and weekend work by pupils.
Across in Renfrewshire, Jim McKechnie of Paisley University has been touring secondaries this term to tell senior pupils about the dangers of part-time work. Almost half of S5 students (46 per cent) have jobs and a further 17 per cent had been working before. Part-time work is far more common than people suspected, according to the latest study in the authority.
There is now clear evidence of the balance to be struck between securing the cash young people need for their social lives and the pay-off in terms of academic performance.
Students who work 1-5 hours a week had an average Higher grade score of 56.8 per cent; those working 6-10 hours 53 per cent; those on 11-15 hours 45.2 per cent; and those working more than 16 hours fared worst at 38.3 per cent.
Dr McKechnie says: "There is a complicated relationship between the amount of time the pupils spend working, the time they spend on homework, their attitude and commitment to school, and their subsequent academic success.
"We have found that working a few hours a week seems to have a beneficial effect. But working more than 10 hours has a negative effect on their academic success."
Fifth-year students generally do shopwork (45 per cent), waiting (17 per cent) and delivery (12 per cent). By S6, working in shops accounts for 64 per cent of jobs. More girls are likely to work than boys. Average weekly earnings for S5 pupils are pound;35.52 but in S6 this rises to pound;48.08. The figures relate to spring 2001.
In fifth year, the majority work on Friday evenings and Saturday and Sunday. A small percentage work before school during the week and one in five work after school.
"The findings indicate that the majority of students are consistent workers. When a student starts to combine work and school they tend to maintain that pattern over time," Dr McKechnie says.
He found, perhaps surprisingly, that there was no evidence between the numbers working within a school and socio-economic indicators such as clothing grants or free school meals among S6 students.
Dr McKechnie's report adds: "In the case of S5 students, a significant result did emerge. However, the pattern of results indicated that students were less likely to work in schools with high indicators of poverty."
"Work and School: Part-time Employment among Senior School Students", by Jim McKechnie, Sue Hill and Sandy Hobbs of Paisley University, was commissioned by Renfrewshire Council.