What is the possible outcome of an ABH case for a juvenile

About 3 months ago my son was arrested for stabbing another pupil at his school. Before I get into the details he was caught on CCTV with the weapon he used, which is a screwdriver, he was also seen approaching the other pupils classroom, shouting at him to get out of the class, having a verbal altercation with him and also stabbing him. The wound was directly above the students eyebrows, which was apparently as the police tells me, a small cut which my son later told me required a few stitches, the wound was quite bad from what my son told me and was a bleeding a lot. My son had a class outside of the main building he told the teachers to let him into the main building to get a cup of water which they did once inside he started shouting at the victim to come out of his class which he didn't hear the victims friends heard my son swearing at the victim and they came out of a separate class and confronted my son they started aggressively walking towards him at which point my son got the screwdriver out of his pocket to defend himself the other students eventually left and my son walked away. The teachers took my son to see the student he was asking to see (the victim) and my son started shouting at the victim behind the locked door, the student then got out of the class and there was a verbal altercation between the two and my son who already had the screwdriver in his hand took a wild stab at student which landed on the victims eyebrow as i said before. In any persons point of view my son was the aggressor and the attack was premeditated to some degree and unprovoked but the reason for the attack is that my son got bullied by these students as the school he goes to only has about 10-20 students all of whom are friends with the victim there's also been one serious fight where my son was attacked by 2 students twice his size. Because of this my son was removed from the school and taught alternitevly for one school year before being forced to return by the headmaster. The attack was a sort of retaliation but my son also brought in the screwdriver for his own safety as he was worried of anothe fight happening. This happened September 2017 and my son is 15 years old. What he did cant be justified but there's two sides two every story. Its been 3 months roughly since his arrest. He's been released on investigation and on the release paper it says hes on investigation for S18 wounding with intent. I've been told the case has been passed onto CPS about 4-8 weeks ago and I'm still waiting for the decision, it's my understanding they have a lot of cases and some cases take priority but this case isn't complete nonsense like a traffic crime or anything surely this would be some near the higher priority case as it's GBH/ABH so whys it taking so long and how Much longer could it take? He hasn't been charged yet so we don't even know if theyre calling it a GBH or ABH. My current solicitor told me it should be ABH as the wound was a small cut but because of the level of intent and premedoration and certain things my son said could it become attempted GBH? What is the likely charge?