But union activists are increasingly in demand as government devolves decision-making to schools.
Academics from Lincoln and De Montfort Universities interviewed 95 National Union of Teachers (NUT) representatives, from school to national level, and found that too much work was regularly cited as a reason why teachers were unwilling to volunteer as union reps.
This fear was justified: the NUT's advice to reps on workforce reform and pay restructuring, for example, ran to 72 pages.
The researchers, who presented findings at this week's American Educational Research Association (AERA) conference in New York, said: "There is an irony that workforce reforms designed ostensibly to reduce teachers' working hours have, to date, had limited impact on the average working week, while potentially adding to the workload of school union reps considerably."
Increased autonomy in schools has also had an impact on activism. Union reps traditionally challenged heads regularly. But now heads have more say on individual teacher's pay, this acts as a "brake on dissent", the researchers said.
Another factor is the league tables: competition makes teachers reluctant to take action that might adversely affect their school. "Industrial action in a competitive market can damage a school's reputation," said the researchers.
As a result, school reps often emerge by default: the only volunteer in a handful of unwilling staff members.
Ironically, more power than ever is being devolved to these reluctant reps. Government reforms have diminished the influence of local authorities, and agreements negotiated between local authorities and unions are no longer binding on schools. Therefore, negotiating power now lies with the school rep.
The researchers concluded: "The importance of these individuals can only increase. If at the same time their effectiveness diminishes, unions (will) face substantial problems protecting their members."
More AERA research, page 30.