Level 4's can do GCSE's with support. My DD is. Her grades won't all be stellar, but in some subjects she is surprising us.
Science for example. Level 4 at end of KS3. Half a term into Y10, getting C's in most things, D in physics (bit too heavy on the Maths, that she has difficulties with).
Catering GCSE (where she wants to head for a career), she is currently getting A's in practical, C's in theory.
Her Maths isn't great, she is currently working on pushing that up to an E, but that is an area she has struggled with her whole life.
English is hovering at about a D right now.
She has been given an extra 25% time in all exams and tests, and a reader to read the questions out to her in exams and tests.
DD's school test every pupil at the end of Y9 to see if they need additional support in their GCSE's, like a scribe, extra time, a laptop or a reader, but I don't know if every school do that routinely on all pupils.
She didn't want to do life skills or ACE, the vocational training programme, as her school doesn't offer the ACE in Catering, and the option open to her were unsuitable.
The only other option was traditional GCSE's.
So, she won't get a clutch of A's. but for every damn grade she has got, she will have worked twice as hard as some A* students!