 Tracking often does not work as effectively as it should because of the composition of the tracks.In practice, tracks are generally not as homogeneous as they could be
(although they are more homogenous than a non-tracking system, which randomly assigns students to classrooms), so some of the potential benefits can't be fully exploited.Even when tracks initially are nearly homogeneous in students' academic abilities, heterogeneity can develop over time, since students learn at different rates.