Over the years, the concept of discrimination and the legal doctrines that protect it, have widened and additional classifications and actions have been recognized as constituting discrimination. This paper explores yet another new category, student ability, and argues that tracking students according to their ability is discriminatory. The analysis in the paper is both philosophical and legal. The philosophical examination applies the different approaches concerning the wrongness of discrimination to the case of ability. The paper then compares case law concerning ability grouping in the United States, Israel and the European Court of Human Rights. While courts in the US and Israel have been reluctant to recognize ability grouping as discriminatory, the ECtHR has struck down ability grouping practices that result in overrepresentation of children from the Roma community in lower tracks and in special education. The paper argues that this approach should be endorsed.