A Primary student should focus on learning, not on competition.
Motivtion should be based on the love of learning itself, not for the sake of getting into an Elite class.
In a mixed ability class, students also learn to respect and appreciate classmates of different strengths.
I still remember when I was in primary school, I was in class "G", Elite class students teased us by calling us "PIG" class.
According to some researches, elite class will not benefit much to the higher ability students but will cause much harm to the lower ability students.
If you believe all students have ability to achieve and they are given equal opportunity of learning since G1, all students can be elites. It's self-confidence that motivates a child to learn and improve.
Elite class system only benefits teachers and school adm.