A new study suggests that college students who take 8 a.m. classes tend to get better grades than those who sleep in.

That might seem obvious: students who manage to show up for an early class are probably keeping saner hours, attending fewer parties and consuming fewer controlled substances than those who schedule around such inconveniences.

Many a college student has discovered, over the course of four years, that no one is forcing anyone to take 8 a.m. classes and that, indeed, one can press on to a bachelor’s degree without having ever attended one. It is not uncommon to see students pushing toward ever-later classes - - and ever-later nights - - over the course of a college career, exercising a freedom they were cruelly denied in high school.

Psychologists at St. Lawrence University found that students who start their college day later in the morning get more sleep. The daily routine of college is not, after all, a particularly punishing schedule. But those students also tend to drink more, to socialize more and, in the long run, to earn lower grades.

Professors Serge Onyper and Pamela Thacher found that students who know they have to get up for an early class keep more sensible hours. They tend to avoid late nights.

Students “who elect earlier classes may be more motivated to find ways to offset the early start time by making healthier choices about their daily living,” Thacher said in a release.

The correlation between later classes and lower grades was modest. The link between later classes and drinking was powerful. Excessive drink is regarded as a strong negative influence on academics. And while late-risers get more sleep, Thacher suspects that sleep may be of lower quality. Heavy drink tends to disrupt sleep.

“Thus, these results indicate that later class start times in college, while allowing for more sleep, also increase the likelihood of alcohol misuse, ultimately impeding academic success,” they wrote in the study.

The study is based on a survey of 253 college students. Students performed cognitive tasks, kept a “sleep diary” and answered questionnaires about daily schedules, drink and substance use and overall mood.

Thacher authored a previous (2007) study that showed college students who stay up all night to finish assignments tend to get lower grades. She said the new study has prompted her to reschedule her own classes.

“Prior to this study, I advocated having classes start later in the morning, so that students could get more sleep,” she said in the release. “But now, I would say that 8 or 8:30 a.m. classes are probably, for some students, going to be a much better choice.”

The study has been presented at an academic conference and have been submitted for publication in the journal Chronobiology International.