CHICAGO, Feb. 6 (Xinhua) -- Students' high school grade point averages are five times stronger than their ACT scores at predicting college graduation, according to a study posted on the website of the University of Chicago (UChicago) Consortium on School Research.

The researchers examined 55,084 students who graduated from Chicago Public Schools of varying academic profiles between 2006 and 2009, and who then immediately enrolled in a four-year college. At the time of the study, all Illinois students took the ACT in the spring of 11th grade.

They found that each incremental increase in GPA is associated with an increase in the odds of graduating college. Across the high schools studied, students with high school GPAs under 1.5 had around a 20-percent chance of graduating from college. For students with GPAs of 3.75 or higher, those chances rose to around 80 percent.

High-school GPAs might be stronger indicators of college readiness because they measure a wider variety of skills, including effort over an entire semester in many different types of classes, and demonstration of academic skills through multiple formats. On the other hand, standardized tests measure a smaller set of skills, and students can prepare for these tests in narrow ways that may not translate into better preparation to succeed in college.

In addition, the researchers found that some students are more likely to graduate college if they come from certain high schools, differences that were not explained by GPAs or ACT scores. These school effects may be the result of more rigorous academic programs at some high schools than others, different non-academic supports for preparing students for college, or simply a tendency of families with more resources for college to send their students to particular high schools.

The study, the first to explicitly test whether standardized assessments are comparable across high schools as measures of college readiness, has been published in Educational Researcher.