Set high A level grades for entry and include several days academic study weekly.
The problem with time out of the classroom for days of academic study, while it sounds reasonable is actually crap for classes and teachers in terms of continuity of teaching, and isn't good for teacher training - you need to teach long sequences of lessons, not just one-offs.
So what would be better would be long periods of time in the classroom, and long periods of time doing academic study. Like maybe, a degree then a PGCE.
Also, no one is going to advise someone with high A-levels to tie themselves into a teaching apprenticeship when the job has such a high rate of attrition. When they drop out, as most of them will, they'll be back where they started, except their high-flying peers will have a decent degree and an entry to a better job market.