Quite. And more than that, you can't move between comps either.
Opponents of grammars are fixated on how unfair it is that a child can be picked for a school at 11 on ability. But ignore hw unfair it is that in the comprehensive system, all children are picked at 11 not on ability, but on house prices/private schol fees.
Basically, under the comp system, the rich get a good education, either directly - they pay for private schols, or indirectly - they pay to live in the catchment for the naice middle class comp.
The ids who live in the rough areas get no options.
At least with grammars, all kids frm all areas can access a top quality education, based on wealth not money.
I'd rather live in a meritocracy over a plutocracy any day.
The 11+ cut-off for grammars could be resolved in many ways - by introducing a 13+ as well for late developers, or using the German system - there is no exam for entry to Gymnasiums, and entry is decided by teacher recommendation instead, based on grade averages etc.
So there is no inherent need in a selective system for a one-day exam to decide children's futures.