Modern education is run with a 'one shoe fits all' approach. We try to cater for boys, girls, those with learning difficulties, those that are gifted, those from impoverished households, those that are affluent, and in general every sector of society that are dumped in our classrooms.
I stand in front of 30 different students, 5 times a day and try my best to educate them all to the best of my ability, and do you know what? Sometimes I don't succeed. It pains me, but some kids slip through the cracks and don't get the education they deserve. I try my best, but there are practicalities that need to be considered.
If you want an education system that caters for all students, regardless of academic ability and socio-economic background then you need to realise that this does not come cheaply. Stick me in a classroom with 10 students instead of 30 and I'll have more time to spend with each one, be better able to take into account their personal education needs, be able to tailor my lessons to individuals rather than focusing on what will suit the majority. Also realise that you'll need to employ three times as many teachers and that the your taxes will need to be substantially increased.
On some level, our modern education system (and previous education systems) fails everyone, to a lesser or greater degree, and few students leave school having reached their full potential. If society wants this to change then the answer is to stop treating schools as a free baby-sitting service, allowing both parents to go out to work and contribute to a nation's GDP, and start treating schools as an investment in a nation's future.