vygotsky's zone of proximal development

Even though not mentioned most time Vygtotsky's Zone of Proximal Development has been widely implemented by teachers and the education system across the world. In Jamaica where I am from, there maybe a Grade 3 class of 35 students and yet three different sections in that one class because the students are grouped according to their ZPD. The teachers responsibility was to diagnose the students level group them accordingly and the lesson and tests would be developed and administered accordingly. Giving a Grade three child who is reading and comprehending at the Grade one level, an inferential question written at the grade three level is asking for frustration and failure, on the other hand you might find one or few student performing way above their grade level and so that child must be taught at that level, s o a teacher may find him or herself with two to three lesson plans and assessment.
I will never foget the first day i went to grade one , my teacher asked me to mentally add 15 +15 mentally and I surprised them and was awarded since i gave the answer without thinking  but then she started giving bigger and bigger numbers I got stuck since the moved out of my ZPD