If Mr Gove re-introduces a two tier exam system - O Levels and CSEs - then those born into poorer or more challenging situations are more likely to be labelled as good for the second tier only. They will be labelled as "not good enough for O Levels" and shunted into the CSE route which will make it even more difficult for them to get on in life - something they might experience for the rest of their lives.
There is evidence that poverty affects educational outcomes - children from poorer families do less well at school. If they are just 'steered' towards CSEs then in many cases it will not be a reflection of the children's latent abilities, but more a reflection of the challenged background into which they were born. They will be labelled and there is no need to do this.
When I attended a very average secondary school in North Yorkshire they ran the old version of the CSEs and O Levels. I did not do well at the time and was' invited' to do CSEs rather than O Levels. Personally I think my poor performance was a result of a bitter, drawn out parental divorce in the run up to the exams. That's not to say I could not have tried harder and parents cannot just leave it all to teachers, but they were too ready to drop us down to do the CSEs rather than ask why some of us were not doing well. The school was 'inspiration free' and younger, newer, teachers seemed to have the optimism knocked out of them soon after arriving. I went on to do O and A Levels and a degree in evening classes later in life, so I think I had the basic ability to do better than they thought.
I suspect some teachers with very large class sizes in busy demanding schools would be tempted to do the same in the future if a two tier examination system is put back in place.
Rather than do the more difficult thing and support pupils to get the best out of them at O Level they would be tempted to steer them towards CSEs which - as I recall were just watered down versions of O Levels and they impressed very few people.
I would be interested to hear any arguments that they were meant to be more practically based, since I don't recall any practical work associated with the old version of the CSE. I suspect CSEs would simply end up being a place where pupils who are not thriving are 'parked' with a pretence that that they are as well regarded as O Levels or are a satisfactory alternative pathway to decent employment prospects.
Why change the system at all? Simply make the current GCSEs harder but allow for different pass levels so that students who are not academically strong can achieve a pass even at a lower level whilst the most talented will still shine. If there must be two different types of qualifications make one of the academic and the other a high quality - skill based qualification not something pretending to be a decent alternative.
I recently spoke to a Head Teacher of a primary school whose pupils in many cases were from difficult backgrounds, and she said that even if a student had parents addicted to drugs or drink or whatever - they still expected them to do their homework and work hard at school. She was against allowing failure to be passed on to children from failing parents.
Teaching looks a hard job to me and I have great respect for what they do - but I fear that some teachers would end up abandoning children who have more challenges in their lives and a second class qualification may well give them an easier way of doing that.