If you bring back grammar schools then you must also bring back technical schools. Selection can only work when there is a wider choice. I speak as one who "failed" the 11-plus and went on to the local secondary modern. I did not feel "written off", because I had a choice of taking the 13-plus exam and going on to the local technical school. My sister, a "late developer", did the same after the 15-plus exam. Both my husband and brother passed the 11-plus and had the choice of grammar or technical schools - both opted for the tech.
By all means have selection but not just at one age (11 years). Children develop at varying stages, so why not a 13-plus and perhaps a 15-plus selection? By bringing in the technical schools as a "middle ground" to the selection you achieve more choice for all and a finer balance between the grammars and comprehensives - thus reducing the "them" and "us" scenario.