The National Education Association, the country's biggest teaching union, believes that nearly 50 per cent of teachers have a second source of income. But Eleanor Hilty, one of the few researchers who has investigated the phenomenon, argues the high rate of moonlighting is more than a reaction to low pay.
"Evidence does suggest that teachers moonlight for economic reasons but it is interesting that the average amount of money they make - approximately $1,001-$3,000 - is rather small," she says in a paper presented to the AERA conference.
After interviewing 12 moonlighters she concluded that the second job often helped compensate for teachers' dissatisfaction with their day job.
One special education teacher told her: "The administrators don't really appreciate my efforts and the children don't provide a lot of the warmth that children in a more normal setting do. My second job gives me a lot of warmth ."
Hilty believes teachers' lack of control over the way they work and the relative loneliness of the job also encourages moonlighting.
"Whether moonlighting hurts the performances of these teachers isn't clear," Hilty says.
"But teaching will remain at best a semi-profession as long as many of its members are doing non-professional work for non-professional wages and benefits."
Correspondence: Eleanor Blair Hilty, Western Carolina University, Cullowhee, North Carolina.