It's no secret to most high school students that taking the required courses, getting good grades and receiving a diploma don't take much work.

The average U.S. high school senior donning a cap and gown this spring will have spent an hour a day on homework and at least three hours a day watching TV, playing video games and pursuing other diversions.

This is sometimes a surprise to adults, particularly state legislators and school board members who thought that by requiring a number of courses in English, math, science and social studies they had ensured that students would dig in and learn what they need to succeed in college.

Guess again, says a new study, "Rigor at Risk: Reaffirming Quality in the High School Core Curriculum," by the Iowa City-based testing company ACT Inc.

"Students today do not have a reasonable chance of becoming ready for college unless they take a number of additional higher-level" courses beyond the minimum, the report said. Even those who do, it concluded, "are not always likely to be ready for college either."

Using research on the college success of students who took the ACT college entrance test, and comparing their test scores to their high school records, ACT researchers found that many core courses were not carefully constructed or monitored and that students often received good grades in the core courses even if they didn't learn much.

State requirements also leave something to be desired, the report said. More than half of the states do not require students to take specific core courses in math or science to graduate.

Many students pick up diplomas having taken "business arithmetic" rather than geometry, or "concepts of physics" rather than a physics course with labs and tough exams.

Taking two years of algebra instead of algebra and geometry and taking chemistry in addition to biology significantly raised the likelihood that a student would score high on the ACT college-readiness scale.

And school officials who look carefully at what is taught in each course, making sure it is what colleges are looking for, are likely to have better results than those who assume the course label is all they need to know, the report concluded.