The part-time job is a rite of passage for most teens. Some are encouraged to work so they'll stop badgering Mom and Dad for money. Others want to save up for college. And with unemployment rates still high in America, many teens work part-time during the school year in an effort to help out with family finances.

But caution is advised: Among high school students, working more than 20 hours a week during the school year can lead to academic and behavior problems.

That's the finding of a new study by researchers at the University of Washington, University of Virginia, and Temple University.

In a reanalysis of longitudinal data collected in the late 1980s, researchers examined the impact of getting a job or leaving work among middle-class teens in 10th and 11th grades.

Drawing from the full sample of about 1,800 individuals, the researchers compared teens who got jobs to similar teens who didn't work, and teens who left jobs to similar teens who kept working.

Using advances in statistical methods, the researchers matched the teens on a long list of background and personality characteristics known to influence whether or not a young person chooses to work.  Using this technique allowed more certainty in estimating the effects of working on teens' development than in the original analysis of the data.

Less engaged 

The researchers found teens who worked more than 20 hours a week were more likely to be less engaged in school, less likely to excel in school, and more likely to fall victim to problem behavior like stealing, carrying a weapon, and using alcohol and illegal drugs.

They also found things didn't get better for those teens when they cut back on work hours or quit working altogether.

However, families in desperate need to extra income, regardless of how much need not worry -- working 20 hours or less a week seemed to have no academic, psychological, or behavioral effect on teens.

Kathryn C. Monahan, a postdoctoral research scientist at the University of Washington, who led the study said working part-time during the school year has been a fixture of American adolescence for more than 30 years and many of today’s teens not only hold part-time jobs, but work over 20 hours a week.

"Although working during high school is unlikely to turn law-abiding teenagers into felons or cause students to flunk out of school, the extent of the adverse effects we found is not trivial, and even a small decline in school engagement or increase in problem behavior may be of concern to many parents," adds Monahan.

The bottom line, suggests Monahan: "Parents, educators, and policymakers should monitor and constrain the number of hours adolescents work while they are enrolled in high school."

The study appears in the January/February issue of Child Development.