A federal judge ruled Friday that a Virginia school system illegally discriminated against Asian Americans when it overhauled the admissions policies at an elite public school. The ruling from U.S. District Judge Claude Hilton found that impermissible “racial balancing” was at the core of the plan to overhaul admissions to Thomas Jefferson High School for Science and Technology, known as “TJ.” The school routinely ranks as the best or one of the best public schools in the country, and slots at the school are highly competitive.