Recently, she says, one of her students pleaded, "Please don't put me on the scale," even though it was clear she had lost weight.
Still, with rates of teen obesity on the rise, new research suggests that a weekly appointment with the bathroom scale may be a low-tech, low-cost tool for helping teens maintain healthy weights.
But some experts caution that weigh-ins should be only one part of a multifaceted approach to weight management.
The new study, published in the Journal of Adolescent Medicine, suggests that overweight teens who step on the scale at least weekly are also more likely to eat less junk food, consume fewer calories, and follow a structured diet. Those in the study who used a scale weekly also engaged in more strenuous physical activity and played fewer video games than non-users.
About 60 percent of those who kept regular appointments with the scale had lost weight during the two years prior to the study, while only 40 percent of infrequent weighers did. However, in this study, the slight difference in weight and body mass index (BMI) that use of the scale appeared to confer was not statistically significant. And even though previous studies have shown that self-weighing is a helpful tool for adults who want to lose weight, only a few studies have been done in adolescents, and the results are mixed.
To complicate matters, other work suggests that frequent scale use may encourage the development of eating disorders.
It's Not About the Weight
Cruthird, for one, feels numbers aren't very important.
"I don't focus on weight loss," she says. "If a kid weighs 250 pounds, and you're telling them they need to be at this weight because of the BMI...they can't grasp needing to lose 75 pounds."
Instead, she stresses attendance in her classes, as well as exercise frequency, duration, and intensity -- the three fitness goals recommended by the U.S. Preventive Services Task Force.
And she says that while scales can be traumatic for some, they also motivate others. She says one of her students, excited at the prospect of weighing herself, couldn't get to the scale fast enough. Cruthird weighs her students on a monthly basis and tells them the numbers -- along with their attendance figures -- so that they can see their progress.
But while scales are part of the picture, Cruthird says that parental involvement in fitness and nutrition is crucial to her students' success.
"Weight loss in general doesn't work unless the person is ready to make change...and then you have to respect the process, that it's not going to happen overnight," she says.
Tipping the Scales... but Not Too Far
Although occasional weighing can give positive feedback, it can have its downsides, too.
"Most eating disorders start with an attempt to lose weight, typically in 7th or 8th grade," says Mary Beth Kavanagh, an instructor of nutrition at Case Western University. "Rapid weight loss, obsession with food and calories, and cutting out entire food groups can be signs that an eating disorder is developing.
"Parents should carefully monitor their teens' dieting behaviors in a non-invasive way and consult a physician at the first signs of unusual behaviors."
She adds that teens are still building bone mass, and if they abandon certain foods such as dairy products in order to lose weight, they may harm themselves.
"Teens who are overweight should consult with a registered dietitian, perhaps in a group class, in order to monitor intake of important nutrients and the rate of weight loss."
Kavanagh says patients with eating disorders often avoid weighing themselves altogether, as they often have an intense fear of weight gain.
Despite these caveats, Kavanagh argues, "most people can benefit from daily weighing. Weight tends to creep up slowly, and discovering small three- to five-pound gains allows for adjusting eating and exercise behaviors to reverse small gains before they become 20-pound gains, which are harder to reverse."
Change on a Larger Scale
Despite the findings of the study, there's disagreement among medical experts on the use of the bathroom scale in treating obesity.
Dr. Paul Shekelle, director of the RAND Corporation's Southern California Evidence-Based Practice Center, says that a population-level approach to fighting obesity, rather than one that targets individual patients, will be critical to reversing the trend.
"It's making the stairs easier to take and the elevator harder to take," he says. "It's more public parkways, city redesign."
Shekelle points to interventions that have helped reduce smoking rates, such as raising cigarette taxes, as useful models. "We have to change the social norms in order to have much success."
Based on the results of the new study, he would not recommend that everyone go out and buy a bathroom scale.
"Could [self-weighing] help? Yeah," he says. "Do I think a national public service campaign [trying to convince] everyone to weigh themselves once a day is going to help? No."