Calculus II was one of the most demoralizing experiences of my college career. I worked hard and still got the worst grades I've ever gotten. In retrospect, I wasn't "bad at math" — I just wasn't as good at remembering formulas and theorems as I was at performing plays in Mandarin or writing essays on the cradle-to-grave environmental costs of a General Electric factory. It was the same thing that had me choking on chemistry exams while I whizzed through the lab portion of the course: Memorization was hard and boring to me, and that felt like being "bad" at math.

When I walked to my overcrowded Calc II lecture twice a week and passed signs for the astrophysics department, I would feel a sickening churn in my gut. I knew I wasn't doing well enough in basic mathematics to ever study the stars. Except I was: I passed the class, probably with a lot less tutoring and cheating than a lot of the people around me, and I could have tightened my pigtails and run full steam into several years of math and physics coursework had I so desired.

According to a study published Wednesday in PLOS ONE, calculus might actually be a common leaky point in the pipeline of women in STEM. The gender gap is closing, but not closed — according to the U.S. Bureau of Labor Statistics, women make up 47 percent of the nation's workforce but just 39 percent of chemists and material scientists, 28 percent of environmental scientists and geoscientists, 16 percent of chemical engineers and 12 percent of civil engineers. Many researchers are looking for the points in a woman's education where she might be unduly discouraged by gender bias. The new study suggests that Calculus I courses in college may be a major turning point.

Lead researcher Jess Ellis, an assistant professor of mathematics at Colorado State University, says she didn't set out to study the gender gap: Her work, funded by the National Science Foundation and conducted under the auspices of the Mathematical Association of America, was focused on understanding the national landscape of calculus as a whole.

Fourteen thousand students across the country were surveyed before and after taking Calculus I (just 5,000 provided complete enough data to be included in the analysis, but that still makes the study the broadest of its kind). They were asked about interest in and intention to pursue STEM degrees, as well as several questions about their test scores, experience and backgrounds.

Ellis wanted to see whether students who planned to "persist" and study Calc II actually followed through on that after taking Calc I, and whether she could find any pattern in their experience that explained why.

"While working with the data we realized there appeared to be a major disparity between genders and decided to investigate it more deeply," Ellis told The Washington Post.

Male and female identified students answered questions about their decision to ditch Calc pretty equally — with one glaring exception:

(Ellis et al, PLOS ONE)

Fewer than one in five of the students who chose not to persist had grades too low to continue (in either gender). But among intended STEM majors, women were more than twice as likely as men to agree with the statement "I do not believe I understand the ideas of Calculus I well enough to take Calculus II."

"As a teacher this is so heartbreaking, but also not as surprising as it should be," Ellis said. "I have had many female students who are strong mathematical thinkers, but don't believe in their mathematical abilities as much as they should."

One could argue, of course, that the women were right — perhaps they really were less likely to understand Calculus than men. But differences in male and female math performance are more cultural than cerebral: Studies have found that men and women alike assume that men will be better at math, and that this bias can even affect the way elementary-school teachers score math homework from young boys and girls. One study found that girls who experienced this bias — where teachers marked equal work from girls with lower grades — did worse in math as they got older, while boys became more confident.

A recent study found that girls were more likely to match boys in math if their parents came from countries with better gender parity. Some researchers even suggest that our country's STEM gap could be the result of a mix of privilege and gender stereotyping: We're a nation that can largely afford to be individualistic, with children seeking out jobs they believe will make them happy and successful. But with so much unconscious bias in classrooms, it's no wonder that many girls think their best chance for success lies anywhere but in the sciences.

Ellis and her colleagues hope that their new data will encourage teachers at all levels — but especially those teaching Calc I — to think of ways to seal up STEM's leaky pipeline. They're also diving deeper into the data for trends of students from minority, lower socioeconomic status and first-generation backgrounds.

But getting women into Calc II won't solve all of science's gender problems. The pipeline is leaking everywhere.

"There is a lot of work that studies men and women's experiences at various stages of the STEM career and indicates different experiences along the way. In the academic faculty setting, these experiences may be related to getting manuscripts reviewed, tenure and promotion decisions, and sabbatical awards. I'm not aware of any of this affecting my work directly, but I am aware that it is a possibility," Ellis said.

That's not to mention the fact that women in STEM fields are likely to face sexual harassment as both students and professors. It's a problem that is being addressed more today than it once was, but there's much work to be done before academia is truly as welcoming to women as it is to men.

There are reasons to want to address this, even if "sexism is bad and should probably go away" doesn't do anything for you. STEM fields are expected to grow so much in the next decade that some million new workers who should be entering scientific careers are missing from the ranks of would-be graduates. The White House has launched initiatives to shuffle these additional STEM workers into the academic pipeline, and working toward gender parity is going to make the talent pool a lot bigger.

"As a community, we need to collectively agree, or listen to what the research has been and continues to tell us, that the population of people in the STEM workforce is not equivalent to the population of people who could be making valuable contributions to the field, and that we stand to gain by having more diverse perspectives in STEM," Ellis said.

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