If counting a standardized test score as 15 percent of a high schooler's final grade were enough to certify she learned what she needed to learn from the course, Texas wouldn't be going through its latest angst about accountability.The tumult over how to factor in end-of-course exams demonstrates vividly the dilemma of high-stakes testing.Broad policies designed to be rigorous and meaningful can run into detrimental real-world ramifications. And officials have to determine how to enforce standards without undermining the system's credibility and effectiveness.When lawmakers and state education officials started talking several years ago about replacing the all-or-nothing Texas Assessment of Knowledge and Skills test with end-of-course exams for high school students, the idea made sense. Instead of having to pass a single comprehensive test to graduate, students all would take the same exam at the end of certain core-subject classes, when the material would be fresh in their minds.Less teaching to the test, too.But students would have to take this exercise seriously for it to accurately measure teaching and learning.When legislation designing the new system was in the works, Sen. Florence Shapiro, a Plano Republican who chaired the Senate Education Committee, insisted that the tests grades count as part of final course grades. Students would have to pass between eight and 12 end-of-course tests, in math, science, English, geography and history.But the Legislature also required that the grade a student made on the State of Texas Assessments of Academic Readiness test account for 15 percent of the overall course grade.A student who fails one of the exams the first time has multiple opportunities to retake it. But individual districts can decide how to count those scores.Districts also could ask the Texas Education Agency to let them waive the 15 percent requirement altogether. And, of course, most of them did.Why? To avoid playing by different rules than anyone else.Course grades affect students' class rankings. And class rankings factor into which colleges students get admitted to and what scholarships they can compete for. If counting STAAR scores up to 15 percent of the class grade would put students at a competitive disadvantage against districts that avoid including them, what's the incentive to give the scores full weight?As it turned out, the TEA didn't implement the 15 percent rule for the 2011-12 school year, when ninth graders were the first class to take STAAR tests instead of TAKS. The rule now has been lifted for 2012-13 as well.Sen. Dan Patrick, R-Houston, new chairman of the education committee heading into next year's session, has pre-filed SB 135, which would give districts the option of counting end-of-course grades for up to 15 percent of a student's final course grade.Expect plenty of debate.The Texas Association of Business has argued against changes that appear to water down accountability standards. The group is correct that Texas schools must do a better job of preparing students for college and a competitive workforce.But will the 15 percent rule accomplish that?If a student fails an end-of-course exam, he might not know the material or he might simply be unprepared on test day. The goal shouldn't be to punish a student but to determine why he wasn't able to pass and better prepare him.For accountability to be meaningful, the tests must be taken seriously. And all districts also must meet the same accountability standards.The Legislature probably will have to set a requirement at something less than 15 percent that makes sense.There is no easy magic to measuring how well public schools and students are performing.