Schoolchildren perform better academically if their teachers are not allowed to enter into collective bargaining deals on pay and conditions, new research suggests.
Barring teachers from being represented by unions can help schools in impoverished areas to close the gap between their academic results and those of schools in wealthier areas, according to a study of educational achievement in the US.
Teaching is one of the most heavily unionised professions in America: around two-thirds of teachers belong to a union, compared with 36 per cent of all public sector employees.
In a paper presented at this week's American Educational Research Association conference, held in Philadelphia, Mark J Fenster, from Notre Dame of Maryland University, looked at maths and literacy test scores for 10- and 14-year-old students across all 50 US states and Washington DC.
When he was collating his data, collective bargaining by teaching unions was mandatory in 35 states, permissible in 11 and illegal in five. The five states where it was banned (Georgia, Texas, South Carolina, North Carolina and Virginia) are among the poorest, with high numbers of students receiving free school meals. Another three states (Indiana, Michigan and Wisconsin) have since outlawed collective bargaining.
Despite their relative poverty, students across all age ranges and subjects show greater levels of improvement in states where unions are not recognised, Professor Fenster has found.
"States with mandatory collective bargaining agreements had a significant advantage, with respect to having students with higher socio-economic status," he writes. "But that higher socio-economic status did not result in higher achievement.
"States permitting collective bargaining agreements.had lower levels of student achievement, especially in mathematics."
Professor Fenster believes that the correlation between collective bargaining and lower results is explained by the fact that unions can delay the implementation of reforms. Government initiatives to improve student performance, such as the No Child Left Behind programme, established in 2001, tend to take longer to be introduced in unionised areas because unions can be reluctant to adopt new assessment methods, he says.
"Union rules may inhibit change and innovation," Professor Fenster writes. "Districts in states with collective bargaining rights may have been slower to respond to a major initiative from the US federal government."
US teachers are also offered tenured positions as a reward for long service, meaning that unions can make it much harder for schools to remove underperforming staff, he adds.
The role of classroom unions has come under particular focus in the US recently, as New York State has approved a plan to allow school districts to use student test scores in teacher evaluations: a proposal bitterly opposed by local unions.
In Colorado, a new bill has proposed that only teachers whose students' grades improve for three consecutive years would be awarded tenure at their schools, and tenure would only be retained if student improvement continued.
In England, the government's introduction of performance-related pay and the abolition of automatic incremental pay rises for teachers have met with strong opposition from classroom unions. In March, members of the NUT took part in a one-day national strike over pay, pensions and working conditions, affecting hundreds of schools across the country.
Professor Fenster examined the national assessment scores of students in all US states. Over the nine-year period of research, students in unionised states consistently underperformed, he found. This was true of those from wealthier backgrounds as well as those receiving free school meals. The performance gaps increased after the passage of the No Child Left Behind Act of 2001.
But Russell Hobby, general secretary of the NAHT headteachers' union in the UK, said that classroom unions in the US had much greater influence over hiring and firing decisions than their British counterparts.
"If unions use collective bargaining power to block legitimate management decisions, then I can see how that would create problems for standards," he said. "But our unions can be positive forces. If they can improve pay and conditions, then that can affect morale. And teachers with higher morale will be more effective and more inspirational in the classroom."